from time import time

vl,vr=map(int,input().split())
v=vl+vr

d=int(input())
w=int(input())
iwl=1/(w+vl);iwr=1/(w+vr)

BEGIN=time()
TIME_LIMIT=1.900
T=0

while time()-BEGIN<=TIME_LIMIT:
    T+=(d-T*v)*iwr
    T+=(d-T*v)*iwl
print(T*w)