
ZOJ Problem Set  1541
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 ith 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). Process to the end of file.
Write to the output file one nonnegative number S  maximal possible area of the working region (in square meters). S must be written with two digits after the decimal point. If it is not possible to construct the fence from the specified blocks, write 0.00.
4
28.00 Source: Northeastern Europe 2001, Northern Subregion 