def main():
    point_a = list(map(float, input().split()))
    point_b = list(map(float, input().split()))

    point_on_y = point_a[1] + \
        point_a[0] * (point_b[1] - point_a[1]) / (point_a[0] + point_b[0])

    print(point_on_y)


if __name__ == "__main__":
    main()