def problem454():
    """


    In the following equation x, y, and n are positive integers.

                                       1   1   1
                                       ─ + ─ = ─
                                       x   y   n

       For a limit L we define F(L) as the number of solutions which satisfy x <
       y ≤ L.

       We can verify that F(15) = 4 and F(1000) = 1069.
       Find F(10^12).
    """

    pass
