#include <bits/stdc++.h>
#define int long long
#define rep(i,n) for(int i=0;i<n;++i)
#define all(a) a.begin(),a.end()
#define P pair<long long,long long>
#define double long double
using namespace std;
signed main(){
  string a;
  cin>>a;
  int b,c;
  rep(i,a.size()){
    if(a.at(i)=='0')
      a++;
  else
    b++;
    }
  cout<<min(a,b)*2;
}

