CF301A Yaroslav and Sequence

Yaroslav has an array, consisting of $ (2·n-1) $ integers. In a single operation Yaroslav can change the sign of exactly $ n $ elements in the array. In other words, in one operation Yaroslav can select exactly $ n $ array elements, and multiply each of them by -1. Yaroslav is now wondering: what maximum sum of array elements can be obtained if it is allowed to perform any number of described operations? Help Yaroslav.

The first line contains an integer $ n $ $ (2

In a single line print the answer to the problem — the maximum sum that Yaroslav can get.

In the first sample you do not need to change anything. The sum of elements equals $ 150 $ . In the second sample you need to change the sign of the first two elements. Then we get the sum of the elements equal to $ 100 $ .