from heapq import heappop,heappush

n,k = map(int,input().split())
A = list(map(int,input().split()))

ans = 0

score = 0
size = 0
h = []

for i in range(n)[::-1]:
    a = A[i]
    if i%2 == 0:
        size += 1
        heappush(h,a)
        score += a

        continue
    # print(i,a,h,score)
    while size > k:
        x = heappop(h)
        size -= 1
        score -= x
    if size == k:
        ans = max(ans,score+a-h[0])
    else:
        ans = max(ans,score+a)
    heappush(h,a)
    score += a
    size += 1
print(ans)