CF588A Duff and Meat

Duff is addicted to meat! Malek wants to keep her happy for $ n $ days. In order to be happy in $ i $ -th day, she needs to eat exactly $ a_{i} $ kilograms of meat. There is a big shop uptown and Malek wants to buy meat for her from there. In $ i $ -th day, they sell meat for $ p_{i} $ dollars per kilogram. Malek knows all numbers $ a_{1},...,a_{n} $ and $ p_{1},...,p_{n} $ . In each day, he can buy arbitrary amount of meat, also he can keep some meat he has for the future. Malek is a little tired from cooking meat, so he asked for your help. Help him to minimize the total money he spends to keep Duff happy for $ n $ days.

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

Print the minimum money needed to keep Duff happy for $ n $ days, in one line.

In the first sample case: An optimal way would be to buy 1 kg on the first day, 2 kg on the second day and 3 kg on the third day. In the second sample case: An optimal way would be to buy 1 kg on the first day and 5 kg (needed meat for the second and third day) on the second day.