N,K=map(int,input().split())
a=list(map(int,input().split()))
ans=0
tmp=0
for i in range(N):
  if i < K:
    tmp+=a[i]
  else:
    if a[i]>0:
      ans+=a[i]
ans+=max(0,tmp)

ans2=0
tmp=0
for i in range(N-1,-1,-1):
  if ans < N-K:
    if a[i]>0:
      ans2+=a[i]
  else:
    tmp+=a[i]
ans2+=max(0,tmp)
print(max(ams2,ans))