const fs = require('fs');
const PREAMBLE_SIZE = 25;

fs.readFile('input', (err, data) => {
  if (err) throw err;
  let input = data.toString().trim().split("\n").map((line) => Number(line) );

  let buf = input.slice(0, PREAMBLE_SIZE);
  for(pos=PREAMBLE_SIZE;pos<input.length;pos++) {
    let next = input[pos];

    let sums = new Set( );
    buf.forEach((a) => buf.forEach((b) => { if (a != b) sums.add(a+b); }));

    if (!sums.has(next)) {
      console.log(next);
      break;
    }

    buf = buf.slice(1, 25);
    buf.push(next);
  }
});