Like everyone, cows enjoy variety.  Their current fancy is new shapes for pastures.  
The old rectangular shapes are out of favor; new geometries are the favorite.

I. M. Hei, the lead cow pasture architect, is in charge of creating a triangular 
pasture surrounded by nice white fence rails.  She is supplied with N (3 <= N <= 40) 
fence segments (each of integer length Li (1 <= Li <= 40) and must arrange them into 
a triangular pasture with the largest grazing area.  Ms. Hei must use all the rails 
to create three sides of non-zero length.

Help Ms. Hei convince the rest of the herd that plenty of grazing land will be available.  
Calculate the largest area that may be enclosed with a supplied set of fence segments.

INPUT FORMAT:

Each testcase:

* Line 1: A single integer N

* Lines 2..N+1: N lines, each with a single integer representing one
          fence segment's length.  The lengths are not necessarily unique.

Input is terminated by end-of-file

SAMPLE INPUT:

5
1
1
3
3
4

OUTPUT FORMAT:

For each testcase:

A single line with the integer that is the truncated integer representation of the 
largest possible enclosed area multiplied by 100.  Output -1 if no triangle of positive 
area may be constructed.

SAMPLE OUTPUT:

692

[which is 100x the area of an equilateral triangle with side length 4]