#define _USE_MATH_DEFINES
#include<stdio.h>
#include<string>
#include<iostream>
#include<cctype>
#include<cstdio>
#include<vector>
#include<stack>
#include<queue>
#include <algorithm>
#include<math.h>
#include<set>
#include<map>
#include<iomanip>

//#include<bits/stdc++.h>



using namespace std;




int main() {
	
	int x=0,y=0;
	int n;
	string p;
	cin>>n>>p;
	for(int i=0;i<n;i++){
		if(p[i]=='0')x++;
		else y++;
		if(x>1||y>1){
			cout<<"YES"<<endl;
			return 0;
		}
	}
	cout<<"NO"<<endl;

	return 0;
}