#!/usr/bin/env python3
import heapq

(n, k), ds = (list(map(int, input().split())) for _ in "..")
end_times, prev, ans = ds[:k], 0, 0
heapq.heapify(end_times)
for t in ds[k:]:
    curr = heapq.heappop(end_times)
    ans = max(ans, curr - prev)
    heapq.heappush(end_times, curr + t)
    prev = curr
while len(end_times) > 1:
    curr = heapq.heappop(end_times)
    ans = max(ans, curr - prev)
    prev = curr
print(ans)