#include <iostream>
#include <string>
#include <cstring>
using namespace std;

int main()
{
	int n;
	string s;

	cin >> n >> s;

	if (n < 2 || s == "101" || "010") {
		cout << "NO" << endl;
	}
	else{
		cout << "YES" << endl;
	}

	return 0;
}