def f(v):
    left, right = 0, d / w
    for _ in range(100):
        mid = (left + right) / 2
        if v * mid + w * mid < d:
            left = mid
        else:
            right = mid
    return right

vl, vr = map(int, input().split())
d = int(input())
w = int(input())
ans, t, p = 0, 0, 0
while d > 0:
    p += 1
    if p % 2:
        t = f(vr)
    else:
        t = f(vl)
    d -= (vl + vr) * t
    ans += w * t
print(ans)