Special Discounts

A Shopkeeper sells $N$ items. Each item costs same number of cents - $X$ cents and there are two types of discounts associated with each item $A[i]$ and $B[i]$ cents. Yash goes to the shop with $Y$ cents in his pocket. He can buy any number of items. Suppose he buys $K$ items with indices $i$$1$ $,$ $i$$2$ $.....$ $i$$K$. Total discount on a set of items is equal to $min$ ($\sum_{j=1}^K$ $A$$i$$j$