Problem Description

Given a year and day difference, compute the resulting date without using built-in date libraries. Handle leap years, month lengths, and year transitions correctly.

Input Format

Three integers: year, month, day, then number of days to add.

Output Format

Resulting date in YYYY-MM-DD format.

Constraints

• 1 ≤ year ≤ 9999

• Valid starting date

• -10000 ≤ day difference ≤ 10000

• Handle leap years correctly

• No built-in date libraries allowed

Sample Input/Output

Explanation

Starting from 2024-02-28, adding 2 days: 2024-02-29 (leap year), then 2024-03-01.