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 fac(n):
    if n == 0:
        return 1
    return n * fac(n - 1)


def main():
    n = int(input())
    print(fac(n))


if __name__ == '__main__':
    main()