from heapq import heapify, heappop, heappush
N, K = map(int, input().split())
A = list(map(int, input().split()))
hp = []
heapify(hp)
s = 0
ans = 0

for i in range(N - 1, -1, -1):
    if (N - 1 - i) < K -1:
        heappush(hp, A[i])
        s += A[i]
    else:
        if i & 1:
            while len(hp) != K - 1:
                a = heappop(hp)
                s -= a
            ans = max(ans, s + A[i])
        heappush(hp, A[i])
        s += A[i] 
print(ans)