#include <cstdio>
#include <iostream>
#include <algorithm>
using namespace std;
int n,a[30*2],sum,sum1,cnt=1;
int main(){
scanf("%d",&n);
for(int i=1;i<=n;i++){scanf("%d",&a[i]);}
while(a[cnt]!=0){sum++; cnt++;}
cnt=n;
while(a[cnt]!=0){sum1++; cnt--;}
if(sum%2==1 || sum1%2==1)puts("YES");
else puts("NO");
return 0;
}