// Amazon is trying to optimize its warehouse inventory for 2-hour delivery items. 
// As part of that effort you are given a real-time stream of individual items ordered
// through Amazon.  Each entry in the stream includes a single item SKU, number
// of those items in the individual order, and a timestamp.
// Write a program, that will store the stream data. This program can also be
// queried, separately, at any time, to return the SKUs for all the items ordered in
// the last 6 hours as well as the combined, overall volume for each item.
// 
// Example data:
// (“ITEM_1”, 5, 1620311721066)
// (“ITEM_2”, 2, 1620311782011)
// (“ITEM_3”, 12, 1620311822562)
// (“ITEM_1”, 14, 1620311851135)
// (“ITEM_4”, 15, 1620311893213)
// (“ITEM_2”, 10, 1620311926421)
// (“ITEM_3”, 6, 1620311979012)
// 
// Output - [(“ITEM_1”, 19), (“ITEM_2”, 12), (“ITEM_3”, 18), (“ITEM_4”, 15)]