50 * 85 * 5 = 21250
So there are 21250 locations where things could be stored.
All you need is 21251(21250 +1) items, and something has to share means Any fewer than 21251 items allows each item to have its own bin, so if we have 21,251 items, the 21,251st item must share a bin with another item.
ans should be 21251.