vl, vr = map(int, input().split())
d = int(input())
w = int(input())
ans = 0

for i in range(10 ** 6):
    if i % 2 == 0:
        t = d / (w + vr)
    else:
        t = d / (w + vl)
    
    d -= t * (vr + vl)
    ans += t * w

print(ans)