from heapq import heapify, heappop, heappush

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

ans = 0
res = 0
H = []
heapify(H)
for i in range(n - 1, -1, -1):
    if i % 2 == 1 and len(H) == k - 1:
        ans = max(ans, res + A[i])
    heappush(H, A[i])
    res += A[i]
    if len(H) == k:
        res -= heappop(H)
print(ans)