FINISH LAB #5

 NEXT: Ask the user to input an integer
      and validate it as greater than 1.

      Call this variable n.

      Use a for loop to calculate the
      sum 1 + 2 + ... + n.

      Use a for loop to calculate n!
      (n-factorial), which is
       1 * 2 * 3 * ... * n.

      Show the results on the console.