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
def f(s, n):
        s *= n
        if n <= 2:
                return s
        else:
                return f(s, n-1)

n = int(raw_input())
s = 1
print f(s, n)