Given an array of integers A of size N and an integer B.
You have to pick some elements from the array A while picking you have to follow the given conditions:

1. The first element to be picked should be A[1]
2. The last element to be picked should be A[n]
3. If you pick some element A[j] after A[i], then it should follow the constraints j-i >= B, j-i <= 2*B

Return the maximum sum of all picked elements.

Note: Array A has 1-based indexing.

Constraints:
1 ≤ N ≤ 10^5
1 ≤ A[I] ≤ 10^5
1 ≤ B ≤ N

Example:
A = [7, 9, 3, 8, 11, 10] , B = 2
Output: 25
Explanation: You pick {7, 8, 10}

Example:
A = [5, 4, 3, 2, 1], B = 1
Output: 15
Explanation: You pick all elements

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