Deepest cut per product

Before a sale, Myntra's pricing team reviews the sharpest single cut each product has already taken this season. A product that has been cut hard once and still did not sell is a candidate for clearance rather than another discount, since repeating a cut that failed costs margin twice.

For each product that was ever cut, return the product_id, the changed_on date of its sharpest single fall, and the size of that fall as drop_amount. If a product took its sharpest cut more than once, report the first time it happened.