from heapq import heappop, heappush
n, k = map(int, input().split())
a = list(map(int, input().split()))
if k == 1: print(max(a[1::2])); exit()
hq = []
s = 0
ans = 0
for i in range(n-1, -1, -1):
    if len(hq) < k-1:
        heappush(hq, a[i])
        s += a[i]
    elif i%2 == 0:
        m = heappop(hq)
        heappush(hq, max(a[i], m))
        s += max(a[i], m)-m
    else:
        ans = max(ans, a[i]+s)
        m = heappop(hq)
        heappush(hq, max(a[i], m))
        s += max(a[i], m)-m
print(ans)