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 Ruby (2.3.3) (judge verdict: Accepted)

##templete
n = gets.chomp.to_i
a = gets.chomp.split(" ").map { |e| e.to_i }

res = []
ans = 0
index = 0
m = 10000000000

def summ(a)
  leng = a.length
  res = 0
  for i in 0..leng-1 do
    res += a[i]
  end
  res
end


for i in 0..n-1 do
  if a[i] < 0
    res[index] = a[i]
    index += 1
  else
    ans += a[i]
    m = a[i] if a[i] < m
  end
end

res = res.sort

leng = res.length

if leng % 2 == 0
  ans -= summ(res)
else
  for i in 0..leng-2 do
    ans += -res[i]
  end

  if -res[leng-1] > m
    ans -= res[leng-1]
    ans -= 2*m
  else
    ans += res[leng-1]
  end
end


puts ans