#!/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 i in range(k, n + k):
    ans, prev = max(ans, (curr := heapq.heappop(end_times)) - prev), curr
    if i < n: heapq.heappush(end_times, curr + ds[i])
print(ans)