import sys
Vl,Vr=map(int,input().split())
d=int(input())
w=int(input())
ans=0
cnt=0
e=10**-7
while d>0:
  if cnt%2==0:
    time=d/(w+Vr)
    ans+=(w*time)
    d-=((Vl+Vr)*time)
    cnt+=1
    if (Vl+Vr)*time<=e:
      print(ans)
      sys.exit()
  else:
    time=d/(w+Vl)
    ans+=(w*time)
    d-=((Vl+Vr)*time)
    cnt+=1
    if (Vl+Vr)*time<=e:
      print(ans)
      sys.exit()
print(ans)