vl, vr = map(int, input().split())
d = int(input())
w = int(input())
sum_d = 0
for i in range(100):
    t1 = d/(w+vl)
    sum_d += t1*w
    d -= t1*(vl+vr)
    t2 = d/(w+vr)
    sum_d += t2*w
    d -= t2*(vl+vr)
print(sum_d)