#include<bits/stdc++.h>
using namespace std;
int main(){
  string s;
  cin >> s;
  int a=0,b=0;
  for(int i=0;i<(int)s.size();++i){
    if(s.at(i)=='0') a++;
    else b++;
  }
  cout << min(a,b)*2 << endl;
}