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 Factorial {
    static void Main() {
        long input;

        input = long.Parse(Console.ReadLine());

        Console.WriteLine(Fact(input));
    }

    static long Fact(long num) {
        if (num == 0)
        {
            return 1;
        }
        else {
            return num * Fact(num - 1);
        }
    }

}