#include<bits/stdc++.h>
using namespace std;
int main(){
  int n;
  int count=0;
  string s;
  cin>>n>>s;
  vector<char> c(n);
  for(int i=0;i<n,i++){
    c[i]=s.at(i);
    if(c[i]=='0'){
      cout++;
    }
  }
  cout<<2*min(count,n-count);
}
  