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
fscanf(STDIN,"%d",$n);
$a=1;
for($i=1;$i<=$n;++$i) $a*=$i;
printf("%.0f",$a);
?>