output_description: Print the factorial of n in a line.
input_description: An integer n (1 ≤ n ≤ 20) in a line.
attempt: print(
      [
          "1",
          "1",
          "2",
          "6",
          "24",
          "120",
          "720",
          "5040",
          "40320",
          "362880",
          "3628800",
          "39916800",
          "479001600",
          "6227020800",
          "87178291200",
          "1307674368000",
          "20922789888000",
          "355687428096000",
          "6402373705728000",
          "121645100408832000",
          "2432902008176640000",
          "51090942171709440000",
      ][int(input())]
  )
  
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"}]