#include<bits/stdc++.h>
using namespace std;
int main(){
	freopen("change.in","r",stdin);
    freopen("change.out","w",stdout);
    int n;
    cin>>n;
    string s;
    cin>>s;
    if(s[0]!=s[1]&&n==2){
        cout<<-1;
        return 0;
    }   
    int t1=0,t0=0;
    for(int i=0;i<s.size();i++){
    	if(s[i]=='1')
    		t1++;
    	if(s[i]=='0')
			t0++;	
	}
	if(t0==0){
		cout<<0;
		return 0;
	} 
	if(t1==0){
		cout<<0;
		return 0;
	}
    if(t1==t0){
        cout<<2;
        return 0;
    }
    else{
        cout<<1;
        return 0;
    }
    return 0;
}