#include <bits/stdc++.h>
#define ll long long
using namespace std;
int main()
{
  string s;
  ll z=0,o=0;
  cin>>s;
  for(ll i=0;i<s.size();i++){if(s[i]=='0')z++;else o++;}
  cout<<min(o,z)*2<<endl;
}
