from heapq import heappushpop, heappush
from itertools import accumulate
n, k = map(int, input().split())
ans = -10 ** 20
h = []
now = 0
for x in accumulate(map(int, input().split())):
    if len(h) == k - 1:
        ans = max(ans, k * x - now)
        now += x + heappushpop(h, -x)
    else:
        now += x
        heappush(h, -x)
print(ans)