// ConsoleApplication1.cpp : This file contains the 'main' function. Program execution begins and ends there.
//

#include <iostream>
using namespace std;
int a[100000] = { 0 };
int main()
{
    int t;
    cin >> t;
    bool flag=1 ;
    for (int i = 0;i < t;i++) {
        cin >> a[i];
    }
    for (int i = 0;i < t-1;i++) {
        if (a[i] < a[i + 1]) {
            flag = 1;
        }
        else {
            flag = 0;
            break;
        }

    }
    if (flag == 1) {
        cout << "YES";
    }
    else {
        cout << "NO";
    }
}