n, m = read_line.split.map(&.to_i)
a = read_line.split.map(&.to_i64)
b = read_line.split.map(&.to_i64)
c = Array.new(n) { |i| {a[i] - b[i], 0i64}.max }
ans = 0i64
sum = (m - 1).times.sum { |i| c[i] }
(m - 1).upto(n - 1) do |i|
  sum += c[i]
  ans = {ans, sum}.max
  sum -= c[i - (m - 1)]
end
puts ans