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;

class ABC_125_D
{
    static void Main(string[] args)
    {
        int N = int.Parse(Console.ReadLine());

        string[] input = Console.ReadLine().Split(' ');
        int[] A = new int[N];
        bool hasZero = false;
        int minusCount = 0;
        for (int i = 0; i < N; i++)
        {
            A[i] = int.Parse(input[i]);
            if(A[i] == 0) hasZero = true;
            if (A[i] < 0) minusCount++;
        }

        if(hasZero)
        {
            long ans = 0;
            for (int i = 0; i < N; i++)
            {
                ans += Math.Abs(A[i]);
            }
            Console.WriteLine(ans);
            return;
        }

        if (minusCount % 2 == 0)
        {
            long ans = 0;
            for (int i = 0; i < N; i++)
            {
                ans += Math.Abs(A[i]);
            }
            Console.WriteLine(ans);
        }
        else
        {
            long ans = 0;
            for (int i = 1; i < N-1; i++)
            {
                ans += Math.Abs(A[i]);
            }

            if (Math.Abs(A[0]) < Math.Abs(A[N - 1]))
            {
                ans += -Math.Abs(A[0]) + Math.Abs(A[N - 1]);
            }
            else
            {
                ans += Math.Abs(A[0]) - Math.Abs(A[N - 1]);
            }

            Console.WriteLine(ans);
        }
    }
}