Codeforces 691A Fashion in Berland

#pragma comment(linker, "/STACK:1024000000,1024000000")
#include<cstdio>
#include<cstring>
#include<cmath>
#include<cstdlib>
#include<algorithm>
#include<vector>
#include<map>
#include<set>
#include<queue>
#include<stack>
#include<iostream>
using namespace std;
typedef long long LL;
const double pi = acos(-1.0), eps = 1e-8;
void File()
{
freopen("D:\\in.txt", "r", stdin);
freopen("D:\\out.txt", "w", stdout);
}
inline int read()
{
char c = getchar();  while (!isdigit(c)) c = getchar();
int x = 0;
while (isdigit(c)) { x = x * 10 + c - '0'; c = getchar(); }
return x;
}

int n,a[1010],sz;

int main()
{
scanf("%d",&n);
for(int i=1;i<=n;i++) {scanf("%d",&a[i]); if(a[i]==1) sz++;}
if(n==1)
{
if(a[1]==1) printf("YES\n");
else printf("NO\n");
}
else
{
if(sz!=n-1) printf("NO\n");
else printf("YES\n");
}

return 0;
}