class Yukicoder
  def initialize
    x1, y1 = gets.chomp.split.map(&:to_i)
    x2, y2 = gets.chomp.split.map(&:to_i)

    if y1 > y2
      a = x1 + x2
      b = y1 - y2

      if x1 > x2
        puts (x1 * Rational(b, a) + y2).to_f
      else
        puts (x2 * Rational(b, a) + y2).to_f
      end
    else
      a = x1 + x2
      b = y2 - y1

      if x1 > x2
        puts (x2 * Rational(b, a) + y1).to_f
      else
        puts (x1 * Rational(b, a) + y1).to_f
      end
    end
  end
end

Yukicoder.new