Problem:
Factorial

Write a program which reads an integer n and prints the factorial of n. You can assume that n ≤ 20.

Input

An integer n (1 ≤ n ≤ 20) in a line.

Output

Print the factorial of n in a line.

Sample Input

5

Output for the Sample Input

120

Solution in C# (judge verdict: Accepted)

using System;
    class Program
    {
        static void Main()
        {
            int number = Convert.ToInt32(Console.ReadLine());
            long fact = GetFactorial(number);
            Console.WriteLine(fact);
        }

        static long GetFactorial(int number)
        {
            if (number == 0)
            {
                return 1;
            }
            return number * GetFactorial(number - 1);
        }
    }