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 AOJ.Volume0
{
    class Factorial
    {
        public static void Main()
        {
            int n = int.Parse(Console.ReadLine());
            long ans = 1;
            for (int i = 2; i <= n; i++) { ans = ans * i; }
            Console.WriteLine(ans);
        }
    }
}