using System;

public class Program

{

    public static void Main()

    {

        int[] numbers = {2,3,4,9};

        if (IsSorted(numbers))

            Console.WriteLine("yes");

        else

            Console.WriteLine("No");

    }

    public static bool IsSorted (int[] nums)

    {

        for (int i=1; i<nums.Length; i++)

        {

            if (!(nums[i] > nums[i-1]))

                return false;

        }

        return true;

    }

}