from heapq import heapify, heappop, heappush
import sys

int1 = lambda x: int(x) - 1

# input = lambda: sys.stdin.buffer.readline()
input = lambda: sys.stdin.readline().rstrip()
ii = lambda: int(input())
i1 = lambda: int1(input())
mi = lambda: map(int, input().split())
mi1 = lambda: map(int1, input().split())
li = lambda: list(mi())
li1 = lambda: list(mi1())
lli = lambda n: [li() for _ in range(n)]

INF = float("inf")
mod = int(1e9 + 7)
# mod = 998244353

n, k = mi()
a = li()
q = []
heapify(q)
ans = 0
s = 0
for i in range(n)[::-1]:
    if i & 1:
        ans = max(ans, s + a[i])
    heappush(q, a[i])
    s += a[i]
    while len(q) >= k:
        s -= heappop(q)
print(ans)