#include <iostream>
#include <algorithm>
#include <vector>
#include <deque>
#include <string>
#include <tuple>
#include <functional>
#include <numeric>
#include <cmath>
#include <iomanip>
#include <map>
#include <random>
//#include "toollib.h"
#define INT_MAX 2147483647
#define Loop(i, n) for(int i = 0; i < (int)n; i++)
#pragma warning (disable:4018)

using namespace std;
typedef long long int lint;

typedef struct {
	int x;
	int y;
}coordinate;

//***** Main Program *****



int main() {
	int N;
	string S;
	cin >> N >> S;
	if (N == 1) cout << "NO" << endl;
	else if (N == 2) {
		if (S == "10" || S == "01") cout << "NO" << endl;
		else cout << "YES" << endl;
	}
	else if (N == 3) {
		if (S == "010" || S == "101") cout << "NO" << endl;
		else cout << "YES" << endl;
	}
	else cout << "YES" << endl;
	return 0;
}