ALGORITHM

STEP 1: Read input (month and year), make sure these are valid 
        and convert to integers

STEP 2: Determine day of week for 1st of the given month and year
        use the code in the hints

STEP 3: Determine number of days in the given month and year
        February will cause trouble!! has 28 days in a non-leap year
        and 29 days in a leap year. We need to determine if the given year
        is a leap year or not

STEP 4: Print calendar.
        - They must be formatted exactly as specified.
        - integer month needs to be converted into a string month
          i.e. 6 becomes June, 8 becomes August ....
        - If first line should be centered then we need to determine
          number of spaces to print before the month
          (20 - letters(month) - digits(year) - 1)//2
        - while printing days, we need to print an extra space for single
          digit days. Also, we have to print newline after saturday!!