using System;

public class Program

{

    public static Main()

    {

        int[] arr = {7, 8, 4, 6, 2, 1};

        Console.Write("The list of numbers: 7,8,4,6,2,1");

        Console.WriteLine();

        int targetNumber= 6;

        Console.Write("Target Number = " + targetNumber);

        Console.WriteLine();

        /*

        int exist = Array.IndexOf(arr, targetNumber);

        if (exist == -1){

            Console.WriteLine("No such a number in list");

        }else{

            Console.WriteLine("Target number found at index: "+ exist);  

        }

        */

        for (int i=0; i< arr.Length; i++){

            if(arr[i] == targetNumber){

                return i;

                //Console.WriteLine("The target number found at index: " +  i); 

            }

​

        }

        return -1;

    }

}