题目描述
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.
Example
Input
5
Output
120
输入格式
见题面
输出格式
见题面
样例输入
5
样例输出
120