from heapq import heappop,heappush

n,k=map(int,input().split())
a=list(map(int,input().split()))

mx=0
hq=[]

sm=0
for i in range(n-1,-1,-1):
  if i%2==1 and len(hq)==k-1:
    mx=max(mx,sm+a[i])
  sm+=a[i]
  heappush(hq,a[i])
  if len(hq)>=k:
    sm-=heappop(hq)

print(mx)