from heapq import *

N,K=map(int,input().split())
A=["*"]+list(map(int,input().split()))

Ans=0
Q=[]; Q_sum=0
for i in range(N,0,-1):
    a=A[i]

    heappush(Q,a); Q_sum+=a

    if len(Q)>K-1:
        b=heappop(Q); Q_sum-=b
        if i%2==0:
            Ans=max(Ans,b+Q_sum)

print(Ans)