PROBLEM STATEMENT

You are given a list of integers, and you are allowed to group elements into pairs.  Each element 
must either belong to a single pair or remain unpaired.  Sum the products of the pairs with the 
values of the unpaired elements.  Your goal is to maximize this sum.


For example, consider the list {0, 1, 2, 4, 3, 5}.  If you make the pairs (2, 3) and (4, 5), the 
sum is 0 + 1 + (2 * 3) + (4 * 5) = 27.


You are given a vector <int> data containing the list of integers.  Return the maximum possible sum.



DEFINITION
Class:CreatePairs
Method:maximalSum
Parameters:vector <int>
Returns:int
Method signature:int maximalSum(vector <int> data)


CONSTRAINTS
-data will contain between 1 and 50 elements, inclusive.
-Each element of data will be between -1000 and 1000, inclusive.


EXAMPLES

0)
{0, 1, 2, 4, 3, 5}

Returns: 27

The example from the problem statement.

1)
{-1, 1, 2, 3}

Returns: 6

If we create a pair (2, 3) we get the sum (-1) + 1 + (2 * 3) = 6.

2)
{-1}

Returns: -1

No pairs can be created, so the answer is -1.

3)
{-1, 0, 1}

Returns: 1

In this case we can create a pair (-1, 0) to make the sum equal to (-1) * 0 + 1 = 1.

4)
{1, 1}

Returns: 2

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