import heapq

N, K = map(int, input().split())
A = list(map(int, input().split()))
B = [0] * (N + 1)
for i, v in enumerate(A):
    B[i + 1] = B[i] + v
ans = -(1 << 60)

pq = []
pq_sum = 0
for X in range(1, N + 1):
    if X >= K:
        ans = max(ans, K * B[X] - pq_sum)
    heapq.heappush(pq, -B[X]) # reversed order
    pq_sum += B[X]
    if len(pq) >= K:
        pq_sum -= -heapq.heappop(pq)
print(ans)