1267：Fence

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.

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).

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.