using System;

public class Program

{

static private ulong fact(ulong a)

{ulong factorial = 1;

ulong i = 1;

do

{factorial = factorial*i;

i++;

}

while(i<=a);

return factorial;

}

​

    public static void Main()

    {

Console.WriteLine(" what number would you like to calculate the factorial of");

ulong num1 = ulong.Parse(Console.ReadLine());

ulong ans = fact(num1);

Console.WriteLine(ans);

​

    }

}