CF16B Burglar and Matches

A burglar got into a matches warehouse and wants to steal as many matches as possible. In the warehouse there are $ m $ containers, in the $ i $ -th container there are $ a_{i} $ matchboxes, and each matchbox contains $ b_{i} $ matches. All the matchboxes are of the same size. The burglar's rucksack can hold $ n $ matchboxes exactly. Your task is to find out the maximum amount of matches that a burglar can carry away. He has no time to rearrange matches in the matchboxes, that's why he just chooses not more than $ n $ matchboxes so that the total amount of matches in them is maximal.

The first line of the input contains integer $ n $ ( $ 1

Output the only number — answer to the problem.