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 C# (Mono 4.6.2.0) (judge verdict: Wrong Answer)

using System;
using System.Collections.Generic;
using System.Linq;

class abc125_D
{
    static void Main(string[] args)
    {
        var QN = readInt();
        var QAs = readLongs();

        var minusCount = 0;
        var foundZero = false;
        var minAbs = 10^9L;
        var absSum = 0L;
        foreach(var a in QAs.Take(QN)) {
            var abs = Math.Abs(a);
            if(a < 0) {
                minusCount++;
                minAbs = Math.Min(minAbs, abs);
            } else if(a == 0) {
                foundZero = true;
            }
            absSum += abs;
        }

        if(foundZero|| minusCount%2 == 0) {
            Console.WriteLine(absSum);
        } else {
            Console.WriteLine(absSum - minAbs*2);
        }

    }

    static int readInt() { return int.Parse(Console.ReadLine()); }

    static int[] readInts() { return Console.ReadLine().Split(' ').Select(s => int.Parse(s)).ToArray(); }

    static long readLong() { return long.Parse(Console.ReadLine()); }

    static long[] readLongs() { return Console.ReadLine().Split(' ').Select(s => long.Parse(s)).ToArray(); }

}