using System;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        Console.WriteLine("Enter a number for summation:");

         int total = 1; 

        string users_number = string.Empty;

        users_number = Console.ReadLine();

        for(int number = 1;  number <= Convert.ToInt32(users_number); number++)

        {

            total = number * total;         

        }

        Console.WriteLine("the total is {0}", total);

    }

}

​