#include <bits/stdc++.h>
using namespace std;
int main() {
  string s;
  int a = 0, b = 0;
  for (int i = 0; i < s.length(); i++) {
    a += s[i] == '1';
    b += s[i] == '0';
  }
  cout << min(a, b) * 2;
  return 0;
}
