#coding:utf-8

n=raw_input().split()
n=map(int,n)
A,B,X,Y=n[0],n[1],float(n[2]),float(n[3])

x=A*Y/B
y=B*X/A

if X < x and Y < y:
	print X+Y
elif X < x and y < Y:
	print X+y
elif x < X and Y < y:
	print x+Y
else:
	print x+y