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

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