import sys
input = sys.stdin.readline
from heapq import *
N,K=map(int,input().split())
A=list(map(int,input().split()))

hp = []
sm = 0
ans = 0
for i in range(N-1,0,-1):
    while len(hp)>=K:
        d = heappop(hp)
        sm -= d
    heappush(hp,A[i])
    sm += A[i]
    if i%2==1:
        ans = max(ans, sm)
print(ans)