import heapq

n,k=map(int,input().split())
a=list(map(int,input().split()));hq=[];c=0;ans=0
for i in range(n-1,-1,-1):
    if len(hq)>=k-1 and i&1:
       ans=max(ans,a[i]+c)
    heapq.heappush(hq,a[i]);c+=a[i]
    if len(hq)==k:
        c-=heapq.heappop(hq)
print(ans)