import heapq
N,K = map(int, input().split())
A = list(map(int, input().split()))
H = []
heapSum = 0
ans = 0
for i in reversed(range(N)):
    if len(H)<K-1:
        heapq.heappush(H,A[i])
        heapSum+=A[i]
    else:
        if i%2==1:
            ans = max(ans,A[i]+heapSum)
        heapSum+=A[i]
        heapq.heappush(H,A[i])
        heapSum-=heapq.heappop(H)
print(ans)