#include <bits/stdc++h>
using namespace std;
int main(){
  string S;
  cin >> S;
  int red = 0, blue = 0;
  for (int i = 0; i < S.size(); i++){
    if (S[i] == '0'){
      red++;
    } else {
      blue++;
    }
  }
  cout << min(red, blue) * 2;
}