The INTEGER-OF-DATE function converts a date in the Gregorian calendar from standard date form (YYYYMMDD) to integer date
form. The type of this function is integer.

- Argument-1 must be an integer of the form YYYYMMDD, whose value is obtained from the calculation:
(YYYY * 10,000) + (MM * 100) + DD.

- YYYY represents the year in the Gregorian calendar. It must be an integer greater than 1600.
- MM represents a month and must be a positive integer less than 13.
- DD represents a day and must be a positive integer less than 32 provided that it is valid for the specified month and year combination.

- The returned value is an integer that is the number of days by which the date represented by argument-1 succeeds December 31, 1600, in the Gregorian calendar.