CF455A Boredom

Alex doesn't like boredom. That's why whenever he gets bored, he comes up with games. One long winter evening he came up with a game and decided to play it. Given a sequence $ a $ consisting of $ n $ integers. The player can make several steps. In a single step he can choose an element of the sequence (let's denote it $ a_{k} $ ) and delete it, at that all elements equal to $ a_{k}+1 $ and $ a_{k}-1 $ also must be deleted from the sequence. That step brings $ a_{k} $ points to the player. Alex is a perfectionist, so he decided to get as many points as possible. Help him.

The first line contains integer $ n $ ( $ 1

Print a single integer — the maximum number of points that Alex can earn.

Consider the third test example. At first step we need to choose any element equal to $ 2 $ . After that step our sequence looks like this $ [2,2,2,2] $ . Then we do $ 4 $ steps, on each step we choose any element equals to $ 2 $ . In total we earn $ 10 $ points.