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(x):
  if x == 0:
    return 1
  else:
    return x * f(x-1)
n = int(input())
print(f(n))