#include <bits/stdc++.h>
using namespace std;
int main() {
  int x, y;
  for (int i = 0; i < 50000; i++) {
    char a;
    a = '2';
    cin >> a;
    if (a == '0') {
      x++;
    } else if (a == '1') {
      y++;
    } else {
      break;
    }
  }
  int ans = min(x, y);
  cout << ans * 2 << endl;
}
