import sys
input = lambda :sys.stdin.readline()[:-1]
ni = lambda :int(input())
na = lambda :list(map(int,input().split()))
yes = lambda :print("yes");Yes = lambda :print("Yes");YES = lambda : print("YES")
no = lambda :print("no");No = lambda :print("No");NO = lambda : print("NO")
#######################################################################
from heapq import *
ans = 0
n,k = na()
k-=1
a = na()
b = [-float("inf")]
for i in range(1,n,2):
    b.append(max(b[-1],a[i]))
s = 0
hq = []
if n % 2:
    hq.append(a[-1])
    s += a[-1]
    while len(hq) > k:
        x = heappop(hq)
        s-=x
    if len(hq) == k:
        ans = max(ans, s + b[-1])

for i in range(n//2-1,-1,-1):
    heappush(hq, a[i*2])
    s += a[i*2]
    heappush(hq, a[i*2+1])
    s += a[i*2 + 1]
    while len(hq) > k:
        x = heappop(hq)
        s-=x
    if len(hq) == k:
        ans = max(ans, s + b[i])

print(ans)