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 OCaml (4.02.3) (judge verdict: Accepted)

(* O(n) *)
let solve n a_s =
  let abs_s = List.map abs a_s in
  let mi = List.fold_left min max_int abs_s in
  let sum = List.fold_left (+) 0 abs_s in
  if mi = 0 then
    sum
  else
    let neg_count = List.fold_left (fun acc a -> if a < 0 then acc + 1 else acc) 0 a_s in
    if neg_count mod 2 = 0 then
      sum
    else
      sum - mi * 2

let read_ints () = read_line () |> Str.split (Str.regexp " ") |> List.map int_of_string
let _ =
  let n = read_int () in
  read_ints () |> solve n |> string_of_int |> print_endline