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

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

H=[]
SUM=0
ANS=0

for i in range(N-1,0,-1):
    if i%2==1 and len(H)==K-1:
        ANS=max(ANS,SUM+A[i])

    heappush(H,A[i])
    SUM+=A[i]
    while len(H)>K-1:
        x=heappop(H)
        SUM-=x

print(ANS)