//#include <bits/stdc++.h>

#include <iostream>

#include <cstdio>

#include <cstring>

#include <algorithm>

#include <cmath>

using namespace std;

#define For(i,j,n) for(int i=j;i<=n;i++)

#define mst(ss,b) memset(ss,b,sizeof(ss));

typedef  long long LL;

template<class T> void read(T&num) {

    char CH; bool F=false;

    for(CH=getchar();CH<''||CH>'';F= CH=='-',CH=getchar());

    for(num=;CH>=''&&CH<='';num=num*+CH-'',CH=getchar());

    F && (num=-num);

}

int stk[], tp;

template<class T> inline void print(T p) {

    if(!p) { puts(""); return; }

    while(p) stk[++ tp] = p%, p/=;

    while(tp) putchar(stk[tp--] + '');

    putchar('\n');

}

//const LL mod=1e9+7;

const double PI=acos(-1.0);

const LL inf=1e18;

const int N=2e5+;

const int maxn=;

const double eps=1e-;

int n,a[];

int main()

{

          read(n);

      int sum=;

      For(i,,n)

      {

        read(a[i]);

        sum+=a[i];

      }

      if(n==)

      {

        if(a[]==)

        cout<<"YES";

        else cout<<"NO";

      }

      else {if(sum==n-)cout<<"YES";

      else cout<<"NO";

    }

        return ;

}