N,K = map(int,input().split())
A = list(map(int,input().split()))
import heapq
now = A[N - K + 1:N]
heapq.heapify(now)
ans = 0
nsum = sum(now)
#print(nsum)
import sys
if K == 1:
    ans = 0
    for i in range(N):
        if i & 1 and A[i] > ans:
            ans = A[i]
    print(ans)
    exit()
i = N - K
for j in range(i,-1,-1):
    if j & 1:
        tmp = nsum + A[j]
        if tmp > ans:
            ans = tmp
    t = heapq.heappop(now)
    if A[j] > t:
        heapq.heappush(now,A[j])
        nsum = nsum - t + A[j]
    else:
        heapq.heappush(now,t)
print(ans)