#便民小题解🚀️ 
#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
ll a[100010];
int main(){
ll n;
cin >>n;
ll h = 0;
for (ll i = 0;i<n;i++){
cin >>a[i];
}
for (int i = 0;i<n;i++){
h += 1;
if (h <= a[i]){
cout <<"NO";
return 0;
}
}
cout <<"YES";
}
//以为······原因暂时不能编写注释，可以看一下↑一个题解