vl,vr = map(int,input().split())
d = int(input())
w = int(input())
vl *= 1000000000
vr *= 1000000000
w *= 1000000000

r = 0
l = d
p = 0
ans = 0
while r < l:
    time = d / (vr + w)
    l2 = vl * time
    r2 = w * time
    ans += r2
    if r2/ans < 10**(-9):
        break
    d = r2 - l2
    r = l2
    l = r2
    vl,vr = vr,vl

print(ans)