vl, vr = map(int, input().split())
d = int(input())
w = int(input())
l_pos, r_pos, bee_pos = 0, d, 0
distance = 0

while (r_pos-l_pos) > 1e-8:
    ok, ng = 0, (r_pos-bee_pos)
    while (ng-ok) > 1e-12:
        mid = (ok+ng) / 2
        b, t = bee_pos+mid*w, r_pos-mid*vr
        if b <= t:
            ok = mid
        else:
            ng = mid

    bee_pos += mid * w
    r_pos -= mid * vr
    l_pos += mid * vl
    distance += mid * w
    #print(distance, l_pos, bee_pos, r_pos)

    ok, ng = 0, (bee_pos-l_pos)
    while (ng-ok) > 1e-12:
        mid = (ok+ng) / 2
        b, t = bee_pos-(mid*w), l_pos+mid*vl
        if t <= b:
            ok = mid
        else:
            ng = mid

    bee_pos -= mid*w
    r_pos -= mid*vr
    l_pos += mid * vl
    distance += mid*w
    #print(distance, l_pos, bee_pos, r_pos)

print(distance)