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

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