import heapq as hq
N, K = map(int, input().split())
A = list(map(int, input().split()))
task = []
s = 0
ans = 0


def push(x):
    global s
    hq.heappush(task, x)
    s += x
    if len(task) >= K:
        s -= hq.heappop(task)


for i in range(N//2*2-1, 0, -2):
    if i+1 < N:
        push(A[i+1])
    ans = max(ans, s+A[i])
    push(A[i])

print(ans)