Pa = [int(i) for i in input().split()]
Pb = [int(i) for i in input().split()]
if Pa[1] < Pb[1]:
    print(Pa[1]+(Pb[1]-Pa[1])/(Pa[0]+Pb[0])*Pa[0])
else:
    print(Pb[1]+(Pa[1]-Pb[1])/(Pb[0]+Pa[0])*Pb[0])