import heapq
N,K = map(int,input().split())
A = list(map(int,input().split()))
heap = []
ans = 0
for i in range(N-1,N-K,-1):
    ans += A[i]
    heapq.heappush(heap,A[i])
cur = N-K
if cur%2==0:
    ans += A[cur]
    heapq.heappush(heap,A[cur])
    ans -= heapq.heappop(heap)
    cur -= 1
ans += A[cur]
cnt = ans
while cur>=3:
    heapq.heappush(heap,A[cur])
    cnt -= heapq.heappop(heap)
    cur -= 1
    cnt += A[cur]
    heapq.heappush(heap,A[cur])
    cnt -= heapq.heappop(heap)
    cur -= 1
    cnt += A[cur]
    ans = max(cnt,ans)
print(ans)