Count the Days Between Two Dates

You are given two calendar dates as strings in YYYY-MM-DD format. Return the number of days between them as a non-negative integer.

You must compute the result without using any built-in date/time or calendar library (e.g., no datetime, java.time, Date, or similar). The only calendar knowledge you may rely on is the standard Gregorian calendar rules given below. Assume a helper that returns the number of days in a given month is something you write yourself.

Calendar rules

• Months have the usual lengths: January 31, February 28 (29 in a leap year), March 31, April 30, May 31, June 30, July 31, August 31, September 30, October 31, November 30, December 31.
• A year is a leap year if it is divisible by 4, except years divisible by 100, unless they are also divisible by 400. So 2000 and 2024 are leap years; 1900 and 2100 are not.

Input

• date1: a string in YYYY-MM-DD format.
• date2: a string in YYYY-MM-DD format.

Both dates are guaranteed to be valid calendar dates between 1900-01-01 and 2100-12-31 inclusive. The dates may be given in either order (date1 is not necessarily earlier than date2).

Output

Return a single integer: the absolute difference in days between the two dates. If the dates are equal, return 0.

Examples

Constraints

• 1900-01-01 <= date1, date2 <= 2100-12-31
• Both inputs are valid dates in YYYY-MM-DD format.
• No date/time library calls are allowed; leap-year handling must be implemented from the rules above.