#include <bits/stdc++.h>
using namespace std;
template <class T>
void read(T& num) {
  char CH;
  bool F = false;
  for (CH = getchar(); CH < '0' || CH > '9'; F = CH == '-', CH = getchar())
    ;
  for (num = 0; CH >= '0' && CH <= '9';
       num = num * 10 + CH - '0', CH = getchar())
    ;
  F && (num = -num);
}
int stk[70], tp;
template <class T>
inline void print(T p) {
  if (!p) {
    puts("0");
    return;
  }
  while (p) stk[++tp] = p % 10, p /= 10;
  while (tp) putchar(stk[tp--] + '0');
  putchar('\n');
}
const double PI = acos(-1.0);
const long long inf = 1e18;
const int N = 2e5 + 10;
const int maxn = 1005;
const double eps = 1e-10;
int n, a[1010];
int main() {
  read(n);
  int sum = 0;
  for (int i = 1; i <= n; i++) {
    read(a[i]);
    sum += a[i];
  }
  if (n == 1) {
    if (a[1] == 1)
      cout << "YES";
    else
      cout << "NO";
  } else {
    if (sum == n - 1)
      cout << "YES";
    else
      cout << "NO";
  }
  return 0;
}
