from heapq import *

N, K = map(int, input().split())
A = list(map(int, input().split()))
H = []
A.reverse()
ans = 0
val = 0
for i in range(N):
    if i % 2 == N % 2:
        if len(H) == K - 1:
            ans = max(ans, val + A[i])
    heappush(H, A[i])
    val += A[i]
    if len(H) == K:
        val -= heappop(H)
print(ans)