#include <bits/stdc++.h>

using namespace std;

int n, flag;

int main() {
    while (~scanf("%d", &n)) {
        flag = 0;
        for (int i = 1, x; i <= n; ++i) {
            scanf("%d", &x);
            if (x == 1) {
                flag = 1;
            }
        }
        puts(flag ? "YES" : "NO");
    }
    return 0;
}