Factorial

Time Limit : 1 sec, Memory Limit : 65536 KB
Japanese version is here

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

Source: PC Koshien 2003 , All-Japan High School Programming Contest, Aizu-Wakamatsu, Japan, 2003
http://www.pref.fukushima.jp/pc-concours/