n,k=map(int,input().split())
a=list(map(int,input().split()))
for i in range(1,n):
  a[i]+=a[i-1]
X=1<<60
a1=-X
a2=0
from heapq import heappush,heappop
q=[]
for i in range(k-1):
  heappush(q,-a[i])
  a2+=a[i]
for i in range(k-1,n):
  a1=max(a1,a[i]*k-a2)
  heappush(q,-a[i])
  a2+=a[i]
  a2-=-heappop(q)
print(a1)