import sys
input = sys.stdin.readline
from heapq import *

N, K = map(int, input().split())
A = list(map(int, input().split()))
pq = []
s = 0

for i in range(N-1, N-K, -1):
    heappush(pq, A[i])
    s += A[i]

ans = 0

for i in range(N-K, -1, -1):
    if i%2==1:
        ans = max(ans, A[i]+s)
    
    if pq[0]<A[i]:
        s -= heappop(pq)
        heappush(pq, A[i])
        s += A[i]

print(ans)