using System;

public class Program

{

    public static void Main()

    {

        System.Console.Write("Please Enter a Number : ");

            int Number = int.Parse(System.Console.ReadLine());

            int i = 1;

            int result = 1;

            if (Number >= 0)

            {

                if (Number == 0)

                {

                    System.Console.WriteLine("1");

                }

                else

                {

                    while (i <= Number)

                    {

                        result *= i;

                        i++;

                    }

                    System.Console.WriteLine(result.ToString());

                }

​

            }

            else

            {

                System.Console.WriteLine("Error");

            }

​

        }

    }

​