CF624B Making a String

You are given an alphabet consisting of $ n $ letters, your task is to make a string of the maximum possible length so that the following conditions are satisfied: - the $ i $ -th letter occurs in the string no more than $ a_{i} $ times; - the number of occurrences of each letter in the string must be distinct for all the letters that occurred in the string at least once.

The first line of the input contains a single integer $ n $ ( $ 2

Print a single integer — the maximum length of the string that meets all the requirements.

For convenience let's consider an alphabet consisting of three letters: "a", "b", "c". In the first sample, some of the optimal strings are: "cccaabbccbb", "aabcbcbcbcb". In the second sample some of the optimal strings are: "acc", "cbc".