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
import sys

def fact(n):
    ret = 1
    if n<1:
        return -1
    elif n==1:
        return 1
    else:
        return n*fact(n-1)

line = sys.stdin.readline()
inp = int(line)
print (fact(inp))