import sys, math
sys.setrecursionlimit(1000000)
INF = 1 << 100
#mod = 1000000007
mod = 998244353
input = lambda: sys.stdin.readline().rstrip()
li = lambda: list(map(int, input().split()))
from heapq import *

N, K = li()
A = li()

if K == 1:
    print(max(A[1:]))
    exit()

hq = []
su = 0
acc = [-INF] * N
for i in range(N)[::-1]:
    a = A[i]
    if len(hq) == K-1:
        x = heappop(hq)
        if x > a:
            heappush(hq, x)
        else:
            heappush(hq, a)
            su += a - x
    else:
        su += a
        heappush(hq, a)
    if len(hq) == K-1:
        acc[i] = su

ans = -INF
for i in range(1, N-1, 2):
    ans = max(ans, A[i] + acc[i+1])

print(ans)