#include <iostream>
#include <cstring>
#include <string>
#include <map>
#include <queue>
#include <set>
#include <cmath>
#include <algorithm>
#include <cstdio>
#include <list>
using namespace std;
#define ll long long
#define inf 0x3f3f3f3f
int i, j, k;
int m, n, p;
int a[10010], b[10010];
int main() {
	int t;
	int flag = 0;
	scanf("%d", &t);
	for (i = 0; i < t; i++) {
		scanf("%d", &a[i]);
	}
	for (i = 0; i < t; i++) {
		if (a[i] == 1) {
			flag = 1;
			break;
		}
	}
	if (flag == 1)
		printf("YES\n");
	else
		printf("NO\n");
	return 0;

}