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;
using System.Collections.Generic;
using System.Linq;

public class Hello
{
    public static void Main()
    {
        long n = int.Parse(Console.ReadLine());
        long factorial = 1;
        for (long i = 1; i <= n; i++)
        {
            factorial *= i;
        }

        Console.WriteLine(factorial);
    }
}