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;
public class ABC125D {
    public static void Main() {
        long N, ans = 0;
        List<long> A = new List<long>();
        N = long.Parse(System.Console.ReadLine());
        string[] str = System.Console.ReadLine().Split(' ');
        foreach (string s in str) {
            A.Add(long.Parse(s));
        }
        long min = Abs(A[0]);
        bool minus = false;
        for(int i = 0; i < A.Count; i++) {
            long a = Abs(A[i]);
            ans += a;
            if (a < min) min = a;
            if (A[i] < 0) minus = !minus;
        }
        if (minus) ans -= min * 2;
        System.Console.WriteLine(ans);
    }
    public static long Abs(long x) {
        if (x < 0) return -x;
        else return x;
    }
}