// c
const solve = (inputs) => {
  const input = inputs.split("\n");
  const arr = [];
  for(let i =0;i < input[0].length; ++i) {
    arr.push(input[0].charAt(i));
  }

  const c1 = arr.reduce((a,b) => a + (b == '0' ? 1 : 0),0);
  const c2 = arr.reduce((a,b) => a + (b == '1' ? 1 : 0),0);
  console.log('%d',Math.min(c1,c2) * 2);
}

solve(require("fs").readFileSync("/dev/stdin", "utf8"));
