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;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text;
using System.Text.RegularExpressions;

namespace AtCoder
{
	public class ABC
	{
		static void Main(string[] args)
		{
			Console.SetOut(new StreamWriter(Console.OpenStandardOutput()) { AutoFlush = false });

			int n = int.Parse(Console.ReadLine());
			long[] a = Console.ReadLine().Split().Select(long.Parse).ToArray();
			long ans = 0;
			long min = long.MaxValue;
			for (int i = 0; i < n - 1; i++) {
				if (a[i] < 0) {
					a[i] = -a[i];
					a[i + 1] = -a[i + 1];
				}
				ans += a[i];
				min = Math.Min(min, a[i]);
			}
			System.Diagnostics.Debug.WriteLine(string.Join(" ", a));
			System.Diagnostics.Debug.WriteLine(min);
			if (a[n - 1] < 0 && min < -a[n - 1]) {
				ans -= min * 2;
				ans += -a[n - 1];
			} else {
				ans += a[n - 1];
			}
			Console.WriteLine(ans);


			Console.Out.Flush();
		}
	}
}