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: Accepted)

using System;

namespace Kyopuro
{
    class Program
    {
        static void Main(string[] args)
        {

            int N = int.Parse(Console.ReadLine());
            int i;
            int count;

            string[] st = Console.ReadLine().Split(' ');

            long ans=0;
            long[] num = new long[N];

            for (i = 0; i < N; i++)
            {
                num[i] = long.Parse(st[i]);
            }
            count = CountMinus(num, N);


            for (i = 0; i < N; i++)
            {
                num[i] = Math.Abs(long.Parse(st[i]));
            }

            Array.Sort(num);

            if (ExistZero(num, N))
            {
                for (i = 0; i < N; i++)
                {
                    ans += Math.Abs(num[i]);
                }
            }
            else if (count == 1)
            {
                ans = num[0] * -1;
                for (i = 1; i < N; i++)
                {
                    ans += Math.Abs(num[i]);
                }
            }
            else
            {
                for (i = 0; i < N; i++)
                {
                    ans += Math.Abs(num[i]);
                }
            }
            Console.WriteLine(ans);
        }





        static int CountMinus(long[] numlist, int N)
        {
            int count = 0;
            int i;

            for (i = 0; i < N; i++)
            {
                if(numlist[i] < 0)
                {
                    count++;
                }
            }
            return count%2;
        }

        static bool ExistZero(long[] numlist, int N)
        {
            bool isExist = false;
            int i;

            for (i = 0; i < N; i++)
            {
                if (numlist[i] == 0)
                {
                    isExist = true;
                }
            }
            return isExist;
        }


    }
}