Fence

Time Limit: 1000MS

Memory Limit: 10000K

Description

Workers are going to enclose a new working region with a fence. For their convenience the enclosed area has to be as large as possible. They have N rectangular blocks to build the fence. The length of the i-th block is Li meters. All blocks have the same height of 1 meter. The workers are not allowed to break blocks into parts. All blocks must be used to build the fence.

Input

The first line of the input file contains one integer N (3 <= N <= 100). The following N lines describe fence blocks. Each block is represented by its length in meters (integer number, 1 <= Li <= 100).

Output

Write to the output file one non-negative number S - maximal possible area of the working region (in square meters). S must be written with at least two digits after the decimal point. If it is not possible to construct the fence from the specified blocks, write 0.00.

Sample Input

4
10
5
5
4

Sample Output

28.00

Hint

Source

N/A

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