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)

def factorial(n)
  a = []
  for i in 1..n
    a.push(i)
  end
  j = a.inject(:*)
  return j
end

while line = gets
  n = line.to_i
  p factorial(n)
end