from heapq import *

n, K = map(int, input().split())
A = list(map(int, input().split()))
tot = 0
l_tot = 0
hq = []

ans = 0
for i, a in enumerate(A[:K], 1):
    ans += i * a
for a in A:
    tot += a

    if len(hq) >= K - 1:
        score = tot * K - l_tot
        ans = max(ans, score)

    l_tot += tot
    heappush(hq, -tot)
    if len(hq) == K:
        l_tot += heappop(hq)

print(ans)