n, l = read_line.split.map(&.to_i)
k = read_line.to_i
a = [0] + read_line.split.map(&.to_i) + [l]

lo = 1
hi = l
while hi - lo > 1
  mid = (lo + hi) // 2
  if ok(mid, a, l, k)
    lo = mid
  else
    hi = mid
  end
end
puts lo

def ok(len, a, l, k)
  n = a.size
  bc = Array.new(n, n + 1)
  right = n - 1
  left = n - 1
  while a[right] - a[left] < len
    left -= 1
  end
  while true
    bc[left] = right - left - 1
    break if left == 0
    left -= 1
    while a[right - 1] - a[left] >= len
      right -= 1
    end
  end
  (n - 2).downto(0) do |i|
    bc[i] = {bc[i], bc[i + 1]}.min
  end
  puts [len, bc]
  left = 0
  right = 1
  while a[right] - a[left] < len
    right += 1
  end
  while right < n - 1
    fc = right - left - 1
    if fc + bc[right + 1] <= (n - 2) - k
      return true
    end
    right += 1
    while a[right] - a[left + 1] >= len
      left += 1
    end
  end
  return false
end