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 Ruby (judge verdict: Accepted)

x = gets.chomp
y = x.to_i
sum = 1
i = 1
while i <= y
 sum *= i
 i += 1
end
puts sum