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 PHP (judge verdict: WA: Presentation Error)

<?php
    $N = trim(fgets(STDIN));
    $n = [];
    for($i = 1; $i <= $N; $i++){
        $n[] = $i;
    }
    echo (array_product($n));