import sys
input = lambda :sys.stdin.readline()[:-1]
ni = lambda :int(input())
na = lambda :list(map(int,input().split()))
yes = lambda :print("yes");Yes = lambda :print("Yes");YES = lambda : print("YES")
no = lambda :print("no");No = lambda :print("No");NO = lambda : print("NO")
#######################################################################
inf = 10 ** 20

n, k = na()
a = na()

b = [0] + a
for i in range(n):
    b[i+1] += b[i]

ans = -inf

from heapq import *
hq = []
z = b[0]
for i in range(1, k):
    heappush(hq, -b[i])
    z += b[i]
# print(b)
for i in range(k, n + 1):
    # print(b[i], z, hq)
    ans = max(ans, b[i] * k - z)
    heappush(hq, -b[i])
    z += b[i]
    x = -heappop(hq)
    z -= x

print(ans)