#include <bits/stdc++.h>

using namespace std;

int main() {
  string s;
  cin >> s;
  int a =0, b = 0;
  for(int i=0; i < s.size(); i++) {
    if(s[i] == '0') a++;
    else b++;
  }
  cout << 2*min(a, b) << endl;
}
