class Calc0208
  def initialize(args)
    args = args.map { |l| l.chomp.split(/\s+/) }
    @x, @y = args.shift.map(&:to_i)
    @x2, @y2 = args.shift.map(&:to_i)
  end

  def run
    x, y = @x.abs, @y.abs
    x2, y2 = @x2.abs, @y2.abs

    c = [x, y].max
    c += 1 if x == y && x2 == y2 && x > x2 && @x / x == @x2 / x2 && @y / y == @y2 / y2
    c
  end
end

puts Calc0208.new(STDIN.readlines).run if __FILE__ == $0