from heapq import *

n, k = map(int, input().split())
A = list(map(int, input().split()))
tot = 0
hq = []
ans = 0
for i in range(n - 1, -1, -1):
    a = A[i]
    tot += a
    heappush(hq, a)
    if len(hq) == k:
        if i & 1:
            ans = max(ans, tot)
        tot -= heappop(hq)
print(ans)