CF525C Ilya and Sticks

In the evening, after the contest Ilya was bored, and he really felt like maximizing. He remembered that he had a set of $ n $ sticks and an instrument. Each stick is characterized by its length $ l_{i} $ . Ilya decided to make a rectangle from the sticks. And due to his whim, he decided to make rectangles in such a way that maximizes their total area. Each stick is used in making at most one rectangle, it is possible that some of sticks remain unused. Bending sticks is not allowed. Sticks with lengths $ a_{1} $ , $ a_{2} $ , $ a_{3} $ and $ a_{4} $ can make a rectangle if the following properties are observed: - $ a_{1}

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

The first line of the output must contain a single non-negative integer — the maximum total area of the rectangles that Ilya can make from the available sticks.