Maximum Spending After Buying Items

Given m shops each represented by a non-increasing list of n item values, you repeatedly pick the current rightmost (smallest remaining) item from any shop on day d and pay value * d; find the interleaving of these per-shop pops that maximizes the total weighted sum. The core challenge is scheduling an order (interleaving) of constrained pops from m stacks to maximize the sum of item values times increasing day multipliers (typical DP/knapsack-like sequencing problem).