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;
namespace Factorial
{
    class Program
    {
        static void Main(string[] args)
        {
            int k = int.Parse(Console.ReadLine());
            long ans = 1;
            for (int i = 1; i <= k; i++)
                ans *= i;
            Console.WriteLine(ans);
        }
    }
}