mod = 998244353


def main():
    import sys
    from heapq import heappop, heappush
    input = sys.stdin.readline

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

    S = 0
    pq = []
    ans = 0
    for i in range(N - 1, -1, -1):
        a = A[i]
        if i & 1:
            ans = max(ans, a + S)

        heappush(pq, a)
        S += a
        if len(pq) >= K:
            t = heappop(pq)
            S -= t
    print(ans)


if __name__ == '__main__':
    main()