#include <bits/stdc++.h>
using namespace std;

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