"use strict"
let fs = require('fs');
let input = fs.readFileSync("/dev/stdin", "utf8").split(/\s/);

const myMin = (a: number, b: number) => a < b ? a : b;
let red = 0, blue = 0;

for(let i=0; i<input[0].length; i++) {
  input[0][i] === '0' ? red++ : blue++;
}

return 2 * myMin(red, blue);