using System;

public class Program

{

    public Boolean isValidMountain(int[] arr){

    int i = 0; 

    while(i < arr.Length && i + 1 < arr.Length && arr[i] < arr[i + 1]){

        i++;

}

    if(i == 0 || i + 1 >= arr.Length){

    return false;

}

    while(i < arr.Length && i + 1 < arr.Length){

    if(arr[i] <= arr[i++ + 1]){

    return false;

}

}

    return true;

}

    public static void Main()

    {

        int[] arr = {1,3,4,2,1};

        Boolean result = isValidMountain(arr);

        Console.WriteLine("is Valid mountian :" + isValidMountain(arr));

    }

}

​