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 aizu
{
    class OnlineJudge
    {
        public static void Main()
        {
            long input = long.Parse(Console.ReadLine());
            for(int i=(int)input-1;i > 1;--i){
                input *= i;
            }
            Console.WriteLine(input);
        }
    }
}