#include <bits/stdc++.h>
using namespace std;
int main() {
int n, a[n], count=0;
cin>>n;
for (int i=0; i<n; i++)
cin>>a[i];
for(int i=0; i<n; i++)
if (a[i]<a[i+1])
count++;
if (count>=4)
cout<<"YES";
else
cout<<"NO";
return 0;
}
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