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: Wrong Answer)

using System;

class Program
{
    static void Main()
    {

        int n = int.Parse(Console.ReadLine());
        int sum = n;

        for (int i = n-1; i >= 1; i--)
        {
            sum = sum * i;
        }

        Console.WriteLine("{0}" ,sum);
    }
}