#include<stdio.h>
int main(){
	int n,x,tol;
	scanf("%d",&n);
	tol=0;
	while(n--)
	{
		scanf("%d",&x);
	if(x==1)
	   tol=tol+1;
	}
	if(tol!=0)
	printf("YES");
	else
	printf("NO");
}