import sys
input = sys.stdin.readline
from heapq import heappop, heappush

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

q = []
qs = 0
ans = 0
for i in reversed(range(N)):
    a = A[i]
    if i%2 == 1:
        ans = max(ans, qs + a)
    heappush(q, a)
    qs += a
    if len(q) >= K:
        qs -= heappop(q)

print(ans)