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)

#pragma warning disable

using System;
using System.Collections;
using System.Collections.Generic;
using System.Diagnostics;
using System.IO;
using System.Linq;
using System.Numerics;
using System.Runtime.Serialization.Formatters.Binary;
using System.Text;
using System.Text.RegularExpressions;


static class MainClass
{
    public static void Main(string[] args)
    {
        var n = Console.ReadLine().ToInt32();
        var an = Console.ReadLine().SplittedStringToInt32List();
        var minuscount = 0;
        var zerocount = 0;
        foreach (var item in an)
        {
            if (item < 0)
            {
                minuscount++;
            }
            else if (item == 0)
            {
                zerocount++;
            }
        }
        if (minuscount % 2 == 0 || zerocount >= 1)
        {
            Console.WriteLine(Sums(an));
        }
        else
        {
            var item1 = an.OrderBy(x => Math.Abs(x)).First();
            an.Remove(item1);
            Console.WriteLine(Sums(an) - Math.Abs(item1));
        }

        Console.ReadLine();
        //var n = Console.ReadLine().ToInt32();
        //var an = Console.ReadLine().SplittedStringToInt32List();
        //var primecount = 0;
        //var primelastind = -1;
        //var ind = 0;
        //foreach (var item in an)
        //{
        //    if (PrimeNumber.IsPrime(item))
        //    {
        //        primelastind = ind;
        //        primecount++;
        //    }
        //    ind++;
        //}
        //if (primecount >= 3)
        //{
        //    Console.WriteLine(1);
        //}
        //else if (primecount == 2)
        //{
        //    if (n == 2)
        //    {
        //        Console.WriteLine(an[0]);
        //    }
        //    else
        //    {
        //        Console.WriteLine(1);
        //    }
        //}
        //else if (primecount == 1)
        //{
        //    var prime = an[primelastind];
        //    an.RemoveAt(primelastind);
        //    var aaa = an[0];
        //    for (int i = 0; i < n - 1; i++)
        //    {
        //        aaa = Lcm(aaa, an[i]);
        //    }
        //    Console.WriteLine(aaa);
        //}
        //else
        //{

        //}
        //Console.ReadLine();
    }


    public static class PrimeNumber
    {

        static long[] seedPrimes = {
        2,3,5,7,11,13,17,19,23,29,31,37,41,43,47,53,59,61,67,71,73,79,83,89,97
    };

        public static bool IsPrime(long num)
        {
            if (num == 1)
                return false;
            if (seedPrimes.Contains(num))
                return true;
            if (seedPrimes.Any(x => num % x == 0))
                return false;

            return (num < 2000000) ? IsPrimeBruteforce(num) : IsPrimeMillarRrabin(num);
        }

        private static bool IsPrimeBruteforce(long num)
        {
            if (num == 1)
                return false;
            if (num != 2 && num % 2 == 0)
                return false;
            if (num != 3 && num % 3 == 0)
                return false;
            if (num != 5 && num % 5 == 0)
                return false;
            long i = 0;
            while (true)
            {
                foreach (var p in seedPrimes.Skip(3).Take(8))
                {
                    var primeCandidte = p + i;
                    if (primeCandidte > Math.Sqrt(num))
                        return true;
                    if (num % (primeCandidte) == 0)
                        return false;
                }
                i += 30;
            }
        }

        private static bool IsPrimeMillarRrabin(long num)
        {
            if (num <= 1)
                return false;
            if ((num & 1) == 0)
                return num == 2;

            if (num < 100 && seedPrimes.Contains((int)num))
                return true;

            var WitnessMax = GetWitnessMax(num);

            long d = num - 1;
            long s = 0;
            while ((d & 1) == 0)
            {
                s++;
                d >>= 1;
            }
            foreach (var w in seedPrimes.Take(WitnessMax))
            {
                if (!MillarRrabin(num, s, d, w))
                    return false;
            }
            return true;
        }


        private static int GetWitnessMax(long num)
        {
            if (num < 2047)
                return 1;
            if (num < 1373653)
                return 2;
            if (num < 25326001)
                return 3;
            if (num < 3215031751)
                return 4;
            if (num < 2152302898747)
                return 5;
            if (num < 3474749660383)
                return 6;
            if (num < 341550071728321)
                return 7;
            if (num < 3825123056546413051)
                return 9;
            return 12;
        }


        private static bool MillarRrabin(long num, long s, long d, long witness)
        {
            long x = ModPow(witness, d, num);
            if (x == 1)
                return true;
            for (long r = 0; r < s; r++)
            {
                if (x == num - 1)
                    return true;
                BigInteger rem;
                BigInteger.DivRem(BigInteger.Multiply(x, x), num, out rem);
                x = (long)(rem);
            }
            return false;
        }

        private static long ModPow(long baseValue, long exponent, long modulus)
        {
            return (long)BigInteger.ModPow(baseValue, exponent, modulus);
        }

    }

    public static int Gcd(int a, int b)
    {
        if (b == 0)
            return a;
        return Gcd(b, a % b);
    }
    public static BigInteger Gcd(BigInteger a, BigInteger b)
    {
        if (b == 0)
            return a;
        return Gcd(b, a % b);
    }

    public static BigInteger Lcm(BigInteger a, BigInteger b)
    {
        return (a * b) / Gcd(a, b);
    }

    public static int Lcm(int a, int b)
    {
        return (a * b) / Gcd(a, b);
    }
    // 素因数分解
    public static List<long> PrimeFactorize(long n)
    {
        var bases = n;
        var num = (long)Math.Pow(n, 0.5);
        var ls = new List<long>();
        for (int i = 2; i <= num; i++)
        {
            if (n % i == 0)
            {
                n = n / i;
                ls.Add(i);
                i--;
                continue;
            }
        }
        long nnn = 1;
        foreach (var item in ls)
        {
            nnn = nnn * item;
        }
        if (nnn != bases)
            ls.Add(n);
        return ls;
    }

    #region
    public static int ParentCount;

    public static int[] Parents;
    public static int[] IfParentsChildrenCount;

    public static int[] Ranks;

    public static void InitializeUnionFind(int N)
    {
        Parents = new int[N];
        Ranks = new int[N];
        IfParentsChildrenCount = new int[N];
        for (int i = 0; i < N; i++)
        {
            Parents[i] = i;
            Ranks[i] = 0;
            IfParentsChildrenCount[i] = 1;
        }
        ParentCount = N + 1;
    }

    public static int Root(int a)
    {
        if (Parents[a] == a)
        {
            return a;
        }
        else
        {
            Parents[a] = Root(Parents[a]);
            return Parents[a];
        }
    }

    public static bool Same(int a, int b)
    {
        return Root(a) == Root(b);
    }

    public static void Unite(int a, int b)
    {
        var parentA = Root(a);
        var parentB = Root(b);
        if (parentA == parentB)
            return;
        if (Ranks[parentA] < Ranks[parentB])
        {
            Parents[parentA] = parentB;
            IfParentsChildrenCount[parentB] += IfParentsChildrenCount[parentA];
            ParentCount -= IfParentsChildrenCount[parentA];

            IfParentsChildrenCount[parentA] = 0;
        }
        else
        {
            Parents[parentB] = parentA;
            if (Ranks[parentA] == Ranks[parentB])
            {
                Ranks[parentA]++;
            }
            IfParentsChildrenCount[parentA] += IfParentsChildrenCount[parentB];
            ParentCount -= IfParentsChildrenCount[parentB];
            IfParentsChildrenCount[parentB] = 0;
        }
    }
    #endregion
    #region ライブラリ

    public static long ToInt64(this string str) => long.Parse(str);
    public static int ToInt32(this string str) => str == "" ? 0 : int.Parse(str);
    public static BigInteger ToBigInteger(this string str) => BigInteger.Parse(str);
    public static List<string> SplittedStringToList(this string str) => str.Split(new[] { ' ' }, StringSplitOptions.RemoveEmptyEntries).ToList();
    public static List<int> SplittedStringToInt32List(this string str) => str.Split(new[] { ' ' }, StringSplitOptions.RemoveEmptyEntries).Select(x => int.Parse(x)).ToList();
    public static List<long> SplittedStringToInt64List(this string str) => str.Split(new[] { ' ' }, StringSplitOptions.RemoveEmptyEntries).Select(x => long.Parse(x)).ToList();
    public static List<BigInteger> SplittedStringToBigInteger(this string str) => str.Split(new[] { ' ' }, StringSplitOptions.RemoveEmptyEntries).Select(x => BigInteger.Parse(x)).ToList();
    public const int INF = int.MaxValue / 4;
    public const long LONGINF = long.MaxValue / 2;
    public const int Mod1e9 = 1000000007;

    public static void PrintArray(char[,] array)
    {
        for (int i = 0; i < array.GetLength(0); i++)
        {
            var sb = new StringBuilder();
            for (int j = 0; j < array.GetLength(1); j++)
            {
                sb.Append(array[i, j]);
            }
            Console.WriteLine(sb.ToString());
        }
    }
    public static int Manhattan(int x1, int x2, int y1, int y2)
    {
        return Math.Abs(x1 - x2) + Math.Abs(y1 - y2);
    }

    public static Dictionary<T, int> ToCountedDictionary<T>(this IEnumerable<T> items)
    {
        var dic = new Dictionary<T, int>();
        foreach (var item in items)
        {
            if (dic.ContainsKey(item))
                dic[item]++;
            else
                dic.Add(item, 1);
        }
        return dic;
    }
    public static Dictionary<TKey, TValue> KeyValuePairListToDictionary<TKey, TValue>(this IEnumerable<KeyValuePair<TKey, TValue>> pairs)
    {
        var dic = new Dictionary<TKey, TValue>();
        foreach (var item in pairs)
        {
            dic.Add(item.Key, item.Value);
        }
        return dic;
    }

    public static long Sums(IEnumerable<int> list)
    {
        var sum = 0l;
        foreach (var item in list)
        {
            sum += Math.Abs(item);
        }
        return sum;
        #endregion
    }

    public static int[] dx = { -1, 1, 0, 0 };
    public static int[] dy = { 0, 0, 1, -1 };

    public static int[] dxx = { 0, 1, 1, 1, 0, -1, -1, -1 };
    public static int[] dyy = { 1, 1, 0, -1, -1, -1, 0, 1 };
}