from heapq import heappush, heappushpop
n, k = map(int, input().split())
sm = 0
q = []
ans = 0
for i, x in reversed(list(enumerate(map(int, input().split()), 1))):
    if len(q) < k - 1:
        heappush(q, x)
        sm += x
    else:
        if i % 2 == 0:
            ans = max(ans, sm + x)
        sm += x - heappushpop(q, x)
print(ans)