Using the following table ([source][1]) write some code that takes the names of two planets and returns the distance between them:

    +-------------------+---------------+
    |      Planets      | Distance (km) |
    +-------------------+---------------+
    | Mercury -> Venus  |      50290000 |
    | Venus -> Earth    |      41400000 |
    | Earth -> Mars     |      78340000 |
    | Mars -> Jupiter   |     550390000 |
    | Jupiter -> Saturn |     646270000 |
    | Saturn -> Uranus  |    1448950000 |
    | Uranus -> Neptune |    1627450000 |
    +-------------------+---------------+

Examples, input then output:

    Mercury, Mars
    170030000

<%%>

    Neptune, Jupiter
    -3722670000

<%%>

    Earth, Earth
    0

Note the negative sign there, as Jupiter comes before Neptune. They are also all integers.

Pluto doesn't have to be included (mostly because of a weird orbit which makes it hard to work out the distance).

By the way, but distances between planets I'm meaning orbits - I don't expect a date and working out where they are.

This is code golf, shortest code wins.

  [1]: http://theplanets.org/distances-between-planets/