## https://yukicoder.me/problems/no/2028

import heapq

def main():
    N, K = map(int, input().split())
    A = list(map(int, input().split()))

    answer = 0
    queue = []
    ans = 0
    for i in reversed(range(1, N, 2)):
        if i + 1 < N:
            a = A[i + 1]
            heapq.heappush(queue, a)
            ans += a
            if len(queue) > K - 1:
                b = heapq.heappop(queue)
                ans -= b

        if len(queue) >= K - 1:
            ans2 = ans + A[i]
            answer = max(answer, ans2)

        a = A[i]
        heapq.heappush(queue, a)
        ans += a
        if len(queue) > K - 1:
            b = heapq.heappop(queue)
            ans -= b

    print(answer)    


        

    



if __name__ == "__main__":
    main()