from time import time

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

d=int(input())
w=int(input())
wl=w+vl;wr=w+vr

BEGIN=time()
TIME_LIMIT=1.800
flag=0
T=0

while time()-BEGIN<=TIME_LIMIT:
    if flag:
        T+=(d-T*v)/wr
    else:
        T+=(d-T*v)/wl
    flag^=1

print(T*w)