import heapq

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

r = (N - K - 1) // 2 * 2 + 1
h = list(A[r + 1:])
heapq.heapify(h)
while len(h) >= K:
    heapq.heappop(h)
s = sum(h)
ans = 0
for i in range(r, -1, -2):
    ans = max(ans, s + A[i])
    if i >= 0:
        p = heapq.heappushpop(h, A[i])
        s += A[i]
        s -= p
    if i - 1 >= 0:
        p = heapq.heappushpop(h, A[i - 1])
        s += A[i - 1]
        s -= p
print(ans)