Problem:
Factorial

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.

Sample Input

5

Output for the Sample Input

120

Solution in Python3 (judge verdict: Accepted)

a = int(input())
res = 1

for i in range(a, 1, -1):
    res *= i

print(res)