## Problem Description

CDGG want to build a new pasture.This pasture is a triangle.He has N board(4<=N<=40),every board has a length,each length is a integer Li(1<=Li<=40),He want to use all the board to build pasture so that the area of pasture is maximum.
Now your task is to help CDGG to build this max pasture and calculate the area.
## Input

The input consists of several test cases. For each case,the first line contains a integer N,indicates the number of board,then follow N lines,each line contains a integer Li indicates the length of board.

## Output

For each case,output a line contain a integer,the max area nultiply by 100 and rounded it down to integer,it means that if the answer is 5.7,you only have to output 5.If the pasture is not exist,please output -1.

## Sample Input

5
1
1
3
3
4

## Sample Output

692

## Source

FZU 2009 Summer Training Qualification -- Hero Revival 1