import heapq
n, k = map(int, input().split())
a = list(map(int, input().split()))
ans = 0
hq = []
for i in range(n - k + 1, n):
    ans += a[i]
    heapq.heappush(hq, a[i])
res = 0
for i in range(n - k, -1, -1):
    if i % 2:
        if res < ans + a[i]:
            res = ans + a[i]
    ans += a[i]
    heapq.heappush(hq, a[i])
    ans -= heapq.heappop(hq)
print(res)