from heapq import heapify, heappop, heappush
N, K = map(int, input().split())
A = [int(a) for a in input().split()]

hq = []
heapify(hq)
s = 0
for i in range(N - K + 1, N):
    heappush(hq, A[i])
    s += A[i]

ans = -1 << 60
for i in range(N - K, -1, -1):
    if i & 1:
        ans = max(ans, s + A[i])
    s += A[i]
    heappush(hq, A[i])
    m = heappop(hq)
    s -= m
print(ans)