#! ruby
# yukicoder My Practice
# author: Leonardone @ NEETSDKASU

A, B, X, Y = gets.chomp.split.map(&:to_f)

case (A / B) <=> (X / Y)

when 0
	puts (X + Y)
	
when 1
	Ya = B * X / A
	puts (X + Ya)

when -1
	Xb = A * Y / B
	puts (Xb + Y)
	
end