v = [int(i) for i in input().split()]
d = int(input())
w = int(input())
s = d * 2 * w**2 / (w + v[0]) / (w + v[1])
r = (w-v[0])*(w-v[1])/(w+v[0])/(w+v[1])
ans = s / (1-r)
print(ans)