How to Solve Maximum Spending After Buying Items Problem

You are given a 0-indexed m * n integer matrix values, representing the values of m * n different items in m different shops. Each shop has n items where the jth item in the ith shop has a value of values[i][j]. Additionally, the items in the ith shop are sorted in non-increasing order of value. That is, values[i][j] >= values[i][j + 1] for all 0 <= j < n - 1. On each day, you would like to buy a single item from one of the shops. Specifically, On the dth day you can: Note that all items are pairwise different. For example, if you have bought item 0 from shop 1, you can still buy item 0 from any other shop. Return the maximum amount of money that can be spent on buying all m * n products.