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 main():
    n = int(input())

    print(fact(n))

def fact(i):
    if i == 0:
        return 1

    return i * fact(i - 1)

if __name__ == '__main__':
    main()