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Problem 1877 MiniSum

## Problem Description

yayamao is so clever that he would like to apply post-graduate of MIT(the Massachusetts Institute of Technology).But all the other teammates think that is impossible and daydreaming. wzc gives yayamao a simple puzzle.If yayamao can solve it quickly, wzc promises to support and help yayamao preparing materials.

The puzzle is that, wzc takes out N cards(1,…,N), each card has an integer number Li written on it.yayamao can choose a real number Xi from each card, but the real number should satisfy that |Xi| <= Li.For all choosen Xi, wzc defines a function F(X1,X2,…,XN) = Σ(Xi * Xj)(i < j) and asks yayamao to find the minimum result of the funcion F.

yayamao is stumped by this puzzle and asks you to help him.Can you quickly solve this problem?

## Input

There are multiple cases ,for each case,

First line is the number of cards N (2 <= N <= 40)

Then following N numbers (L1,L2,…LN) that Li (1 <= Li <= 100) is the number written on the ith card.

There may be one or more blank lines between each input case.

## Output

For each case

Output the minimum result of the function F by choosing the group of (X1,X2,…XN). which is rounded to two digits after the decimal point.

2 2 4 3 1 2 3

-8.00 -7.00

## Source

code6

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