#include <bits/stdc++.h>
#define LL long long
using namespace std;
const int N = 1e3 + 10;
const int INF = 0x3f3f3f3f;
int num [N] , last , n , maxc = -INF;
int main()
{
	cin >> n;
	for(int i = 1; i <= n; i++)
		cin >> num[i];
	last = num[1];
	for(int i = 2; i <= n; i++)
	{
		if(num [i] > last)
		{
			if(num[i] < maxc)
			{
				cout << "NO";
				return 0;
			}
		}
		else
		{
			last = num[i];
			maxc = max(maxc,num[i]);
		}
	}
	cout<<"YES";
	return 0;
}