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