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++14 (GCC 5.4.1) (judge verdict: Accepted)

 #include <bits/stdc++.h>
 #include <string> 
 #include <math.h>
 #include <bitset>
 using namespace std;
 
 int main(){
    long long i;
    long long N;
    long long A[120000];
    long long min;
    long long ans = 0;
    long long cnt = 0;

    cin >> N;
    for (i=0; i<N; i++){
        cin >> A[i];
    }

    min = abs(A[0]);

    for (i=0; i<N; i++){
        ans = ans + abs(A[i]);
        if (A[i] < 0)
            cnt++;
        if (min > abs(A[i]))
            min = abs(A[i]); 
    }

    if (cnt%2 != 0)
        ans = ans - min*2;

    cout << ans << endl;
        
    return 0;
 }