Problem:
Score : 400 points

Problem Statement

There are N integers, A_1, A_2, ..., A_N, arranged in a row in this order.

You can perform the following operation on this integer sequence any number of times:

Operation: Choose an integer i satisfying 1 \leq i \leq N-1. Multiply both A_i and A_{i+1} by -1.

Let B_1, B_2, ..., B_N be the integer sequence after your operations.

Find the maximum possible value of B_1 + B_2 + ... + B_N.

Constraints

All values in input are integers.

2 \leq N \leq 10^5

-10^9 \leq A_i \leq 10^9

Input

Input is given from Standard Input in the following format:

N
A_1 A_2 ... A_N

Output

Print the maximum possible value of B_1 + B_2 + ... + B_N.

Sample Input 1

3
-10 5 -4

Sample Output 1

19

If we perform the operation as follows:

Choose 1 as i, which changes the sequence to 10, -5, -4.

Choose 2 as i, which changes the sequence to 10, 5, 4.

we have B_1 = 10, B_2 = 5, B_3 = 4. The sum here, B_1 + B_2 + B_3 = 10 + 5 + 4 = 19, is the maximum possible result.

Sample Input 2

5
10 -4 -8 -11 3

Sample Output 2

30

Sample Input 3

11
-1000000000 1000000000 -1000000000 1000000000 -1000000000 0 1000000000 -1000000000 1000000000 -1000000000 1000000000

Sample Output 3

10000000000

The output may not fit into a 32-bit integer type.

Solution in Haskell (GHC 7.10.3) (judge verdict: Accepted)

import Data.List
import Data.Array.IArray

solve :: [Int] -> Int
solve a = dp!(n,0)
  where
    n = length a
    aa = listArray (1,n) a :: Array Int Int
    k = ((1,0),(n,1))
    dp = listArray k $ map f (range k) :: Array (Int,Int) Int
    f (1,0) = aa!1
    f (1,1) = aa!1 * (-1)
    f (i,0) = max (dp!(i-1,0) + (aa!i)) (dp!(i-1,1) - (aa!i))
    f (i,1) = max (dp!(i-1,0) - (aa!i)) (dp!(i-1,1) + (aa!i))

main :: IO ()
main = do
    _ <- getLine
    a <- map read . words <$> getLine :: IO [Int]
    print $ solve a