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 L_{i} 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 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 ≤ L_{i} ≤ 100).

### Output

Write one non-negative 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.

### Sample

input | output |
---|

4
10
5
5
4 | 28.00 |

**Problem Author: **Nick Durov

**Problem Source: **ACM ICPC 2001. Northeastern European Region, Northern Subregion