# frozen_string_literal: true
# This file is expanded by nanacl.

main = -> do # =================================================================
# frozen_string_literal: true
# require "nanacl/array_sum" # (expanded: L25)
in_n, in_m = gets.chomp.split.map(&:to_i)
in_a = gets.chomp.split.map(&:to_i)
in_b = gets.chomp.split.map(&:to_i)

positives = in_a.zip(in_b).map { |a, b| [a - b, 0].max}

max = 0
(in_n - in_m + 1).times do |i|
  max = [
    max,
    positives.sum_in_range((i)..(i+in_m-1))
  ].max
end
puts max

end # --------------------------------------------------------------------------

# === dependencies -------------------------------------------------------------
# == nanacl/array_sum from main ------------------------------------------------
# frozen_string_literal: true
class Array
  def sum_in_range(range)
    unless @sums
      @sums = [0]
      sum = 0
      each { |v| @sums << (sum += v) }
    end
    range_begin = range.begin || 0
    if range.end.nil?
      @sums[length] - @sums[range_begin]
    elsif range.exclude_end?
      @sums[range.end] - @sums[range_begin]
    else
      @sums[range.end + 1] - @sums[range_begin]
    end
  end
end


# ==============================================================================

main.call