output_description: Print the factorial of n in a line.
input_description: An integer n (1 ≤ n ≤ 20) in a line.
attempt: s = int(input())
  k = 1
  for i in range(2, s + 1):
      k *= i
  print(k)
  
problem_description: Factorial
  
  Write a program which reads an integer n and prints the factorial of n. You
  can assume that n ≤ 20\.
samples: [{"input": "", "output": "0"}]