main.py

N, C = map(int, input().split())
Pos = [int(input()) for _ in range(N)]

Pos.sort()

left, right = 1, 10 ** 9

answer = -1

while left <= right:
    mid = (left + right) // 2

    setting = 1
    last_set_pos = Pos[0]

    for i in range(1, N):
        if Pos[i] - last_set_pos >= mid:
            last_set_pos = Pos[i]
            setting += 1

    if setting >= C:
        answer = mid
        left = mid + 1
    else:
        right = mid - 1

print(answer)