destructuring

const readline = require("node:readline/promises");
const rl = readline.createInterface({
  input: process.stdin,
  output: process.stdout,
});

const /* prettier-ignore */ stages = [

  // Stage 0
  (json) => {
    const { a: _0, b: _1 } = json;
    return [_0, _1];
  },

  // Stage 1
  (json) => {
    const [, , _0, _1, _2, , , _3, _4] = json;
    return [_0, _1, _2, _3, _4];
  },

  // Stage 2
  (json) => {
    const {a: [, , { b: _0, c: [{ d: _1 }] }] } = json;
    return [_0, _1];
  },

  // Stage 3
  (json) => {
    const { a: { a: { a: { a: _0, b: _1 }, b: { a: _2, b: _3 }, c: [, _4, , _5, _6] }, b: [{ a: _7 }, [_8, _9, _10, , _11]] } } = json;
    return [_0, _1, _2, _3, _4, _5, _6, _7, _8, _9, _10, _11];
  },

  // Stage 4
  (json) => {
    const { a: [{ a: { a: { a: [{ a: _0, b: { a: _1, b: [[{ a: _2, b: _3, c: _4 }, ], , _5, , { a: _6, b: _7 }], c: _8 } }, { a: [, , { a: _9, b: _10, c: _11 }], b: { a: _12, b: { a: _13, b: { a: _14, b: _15 } }, c: _16 } }, _17, { a: [, _18], b: { a: { a: { a: _19, b: _20, c: _21 } }, b: _22 } }] }, b: { a: { a: { a: { a: _23, b: _24, c: _25 }, b: { a: _26, b: _27, c: { a: { a: _28, b: _29 }, b: { a: _30, b: _31 }, c: _32 } } }, b: [{ a: { a: _33, b: [{ a: _34, b: _35 }, _36], c: { a: _37, b: [_38, _39, _40], c: { a: _41, b: _42, c: _43 } } }, b: [, _44, [{ a: _45, b: _46, c: _47 }, [_48, _49], { a: _50, b: _51, c: _52 }, _53, ]], c: [_54, _55] }, { a: { a: _56, b: { a: { a: _57 }, b: _58 } }, b: _59 }, { a: _60 }, { a: { a: _61, b: { a: _62, b: _63 }, c: { a: _64, b: _65 } }, b: _66 }], c: _67 }, b: { a: { a: { a: _68, b: _69, c: _70 }, b: _71, c: { a: _72 } }, b: { a: _73 }, c: { a: _74, b: _75, c: { a: _76, b: { a: _77, b: { a: _78, b: { a: _79 } }, c: { a: _80, b: _81, c: [_82, _83] } }, c: _84 } } }, c: { a: { a: { a: _85 }, b: _86 }, b: { a: _87 } } }, c: [{ a: { a: [, ], b: [_88, _89, , { a: _90, b: { a: { a: _91, b: _92 }, b: _93, c: _94 } }] }, b: { a: { a: [{ a: [_95, _96, _97, _98], b: _99, c: _100 }, _101] }, b: _102, c: { a: _103 } }, c: [_104, [_105, { a: _106, b: [{ a: _107 }, _108, _109, ], c: _110 }, , { a: { a: _111, b: _112, c: _113 }, b: _114 }, _115], { a: { a: { a: _116 }, b: { a: _117, b: _118 }, c: _119 } }] }, { a: _120 }, , ] } }, ], b: { a: [, { a: { a: { a: _121, b: _122 }, b: { a: { a: _123, b: { a: { a: _124 } }, c: { a: _125 } } } } }, { a: { a: { a: { a: _126, b: _127, c: _128 } }, b: _129, c: { a: { a: { a: { a: { a: _130, b: { a: _131, b: _132 } }, b: _133 }, b: { a: [{ a: _134 }, _135, _136, , ], b: _137 }, c: _138 }, b: { a: _139, b: { a: { a: _140, b: _141, c: _142 } }, c: _143 } }, b: { a: _144, b: [{ a: _145 }, _146, [_147, _148, _149, [_150, _151, _152, { a: _153, b: _154 }, ], _155], { a: { a: _156 }, b: _157 }] }, c: _158 } }, b: { a: _159 }, c: [, [{ a: { a: _160, b: { a: [{ a: _161, b: _162 }, _163, _164], b: _165 }, c: _166 }, b: { a: { a: { a: _167 }, b: _168 }, b: _169, c: { a: { a: _170, b: [_171, _172, _173, _174, _175] } } } }, { a: [, _176, , { a: _177, b: { a: _178 } }], b: { a: _179, b: { a: _180, b: _181, c: _182 } } }, , { a: { a: _183, b: _184, c: _185 }, b: [{ a: _186 }, , _187] }, ], _188, , { a: { a: [_189, _190, _191, ], b: { a: _192 } } }] }], b: [, [, { a: { a: { a: _193, b: { a: _194 }, c: _195 }, b: _196, c: _197 } }], { a: { a: _198 }, b: { a: [{ a: _199, b: { a: { a: { a: _200, b: _201 }, b: _202, c: _203 } } }, , _204] } }, { a: { a: _205, b: [, _206] }, b: [_207, [{ a: { a: { a: _208 } }, b: { a: _209, b: { a: _210, b: { a: _211, b: { a: _212, b: _213, c: _214 } }, c: _215 } }, c: { a: _216, b: { a: [_217, _218, { a: _219, b: _220 }], b: _221, c: { a: _222 } } } }, { a: [_223, _224, { a: _225 }, { a: _226, b: { a: { a: _227, b: _228, c: _229 }, b: { a: _230, b: _231, c: _232 } } }], b: _233 }, [, ]], [[_234, [{ a: { a: _235 }, b: _236, c: _237 }, _238, { a: _239 }, ]], _240, ], _241], c: [[_242, { a: { a: { a: _243, b: _244 }, b: _245 }, b: [[{ a: _246, b: _247, c: _248 }, _249], _250, ], c: { a: _251 } }, [_252, ]], { a: _253, b: { a: _254, b: _255, c: { a: _256, b: _257 } } }] }, [, ]], c: [[_258, { a: { a: { a: _259, b: [, _260] }, b: [_261, { a: { a: _262, b: [_263, , _264, { a: _265 }], c: _266 }, b: { a: [_267, _268, , { a: _269 }, _270], b: { a: _271 } }, c: [_272, _273] }, _274, { a: { a: { a: [_275, _276, , _277], b: { a: _278, b: _279, c: _280 } }, b: _281, c: _282 }, b: _283, c: { a: { a: _284, b: _285 } } }] }, b: { a: [{ a: _286, b: { a: [{ a: _287, b: _288 }, _289] } }, { a: _290 }], b: _291 }, c: { a: { a: [{ a: _292, b: [{ a: _293, b: _294 }, _295, _296, _297, _298] }, , _299, { a: _300, b: _301 }], b: { a: [_302, { a: [_303, , ], b: _304, c: _305 }], b: _306, c: { a: _307, b: _308, c: [{ a: _309, b: _310 }, , ] } } }, b: { a: _311, b: { a: _312, b: _313 }, c: { a: _314, b: { a: _315 }, c: { a: _316, b: _317 } } }, c: { a: _318 } } }, { a: { a: { a: _319, b: [[_320, { a: _321, b: { a: _322, b: _323 } }, { a: { a: _324, b: _325 } }, _326], { a: _327, b: _328, c: _329 }, ], c: { a: [_330, _331] } }, b: _332, c: [_333, _334, _335, { a: _336, b: { a: _337 } }, _338] } }], { a: [{ a: _339 }, [_340, _341, _342, { a: { a: { a: { a: { a: _343, b: _344, c: _345 }, b: [, _346, , _347] }, b: [_348, _349, _350] }, b: _351, c: _352 }, b: _353 }, { a: { a: { a: [_354, _355, _356], b: { a: _357, b: _358, c: { a: _359 } }, c: _360 } }, b: _361, c: [{ a: { a: _362 }, b: [_363, { a: _364 }, { a: _365 }] }, _366, _367, _368, [{ a: _369, b: _370 }, , _371]] }]] }, { a: { a: _372 }, b: _373 }] } } = json;
    return [_0, _1, _2, _3, _4, _5, _6, _7, _8, _9, _10, _11, _12, _13, _14, _15, _16, _17, _18, _19, _20, _21, _22, _23, _24, _25, _26, _27, _28, _29, _30, _31, _32, _33, _34, _35, _36, _37, _38, _39, _40, _41, _42, _43, _44, _45, _46, _47, _48, _49, _50, _51, _52, _53, _54, _55, _56, _57, _58, _59, _60, _61, _62, _63, _64, _65, _66, _67, _68, _69, _70, _71, _72, _73, _74, _75, _76, _77, _78, _79, _80, _81, _82, _83, _84, _85, _86, _87, _88, _89, _90, _91, _92, _93, _94, _95, _96, _97, _98, _99, _100, _101, _102, _103, _104, _105, _106, _107, _108, _109, _110, _111, _112, _113, _114, _115, _116, _117, _118, _119, _120, _121, _122, _123, _124, _125, _126, _127, _128, _129, _130, _131, _132, _133, _134, _135, _136, _137, _138, _139, _140, _141, _142, _143, _144, _145, _146, _147, _148, _149, _150, _151, _152, _153, _154, _155, _156, _157, _158, _159, _160, _161, _162, _163, _164, _165, _166, _167, _168, _169, _170, _171, _172, _173, _174, _175, _176, _177, _178, _179, _180, _181, _182, _183, _184, _185, _186, _187, _188, _189, _190, _191, _192, _193, _194, _195, _196, _197, _198, _199, _200, _201, _202, _203, _204, _205, _206, _207, _208, _209, _210, _211, _212, _213, _214, _215, _216, _217, _218, _219, _220, _221, _222, _223, _224, _225, _226, _227, _228, _229, _230, _231, _232, _233, _234, _235, _236, _237, _238, _239, _240, _241, _242, _243, _244, _245, _246, _247, _248, _249, _250, _251, _252, _253, _254, _255, _256, _257, _258, _259, _260, _261, _262, _263, _264, _265, _266, _267, _268, _269, _270, _271, _272, _273, _274, _275, _276, _277, _278, _279, _280, _281, _282, _283, _284, _285, _286, _287, _288, _289, _290, _291, _292, _293, _294, _295, _296, _297, _298, _299, _300, _301, _302, _303, _304, _305, _306, _307, _308, _309, _310, _311, _312, _313, _314, _315, _316, _317, _318, _319, _320, _321, _322, _323, _324, _325, _326, _327, _328, _329, _330, _331, _332, _333, _334, _335, _336, _337, _338, _339, _340, _341, _342, _343, _344, _345, _346, _347, _348, _349, _350, _351, _352, _353, _354, _355, _356, _357, _358, _359, _360, _361, _362, _363, _364, _365, _366, _367, _368, _369, _370, _371, _372, _373];
  },

];

(async () => {
  for (const [index, run] of Object.entries(stages)) {
    console.log(`Stage: ${index}`);
    console.log(run.toString().split("\n")[1].trim());

    const json = await rl.question("json> ").then(JSON.parse);
    if (run(json).every((x, i) => x === i)) {
      console.log("Nice!");
      console.log();
    } else {
      throw new Error("Failed...");
    }
  }

  console.log(`Here's your flag: ${process.env.FLAG}`);
})()
  .catch(console.error)
  .finally(() => rl.close());

{"a":0,"b":1}

[null,null,0,1,2,null,null,3,4]

{"a":[null,null,{"b":0,"c":[{"d":1}]}]}

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