## \-\-- Day 4: The Ideal Stocking Stuffer \-\--

Santa needs help [mining](https://en.wikipedia.org/wiki/Bitcoin#Mining)
some AdventCoins (very similar
to [bitcoins](https://en.wikipedia.org/wiki/Bitcoin)) to use as gifts
for all the economically forward-thinking little girls and boys.

To do this, he needs to find [MD5](https://en.wikipedia.org/wiki/MD5)
hashes which, in
[hexadecimal](https://en.wikipedia.org/wiki/Hexadecimal), start with at
least *five zeroes*. The input to the MD5 hash is some secret key (your
puzzle input, given below) followed by a number in decimal. To mine
AdventCoins, you must find Santa the lowest positive number (no leading
zeroes: `1`, `2`, `3`, \...) that produces such a hash.

For example:

-   If your secret key is `abcdef`, the answer is `609043`, because the
    MD5 hash of `abcdef609043` starts with five zeroes
    (`000001dbbfa...`), and it is the lowest such number to do so.
-   If your secret key is `pqrstuv`, the lowest number it combines with
    to make an MD5 hash starting with five zeroes is `1048970`; that is,
    the MD5 hash of `pqrstuv1048970` looks like `000006136ef...`.

## \-\-- Part Two \-\-- {#part2}

Now find one that starts with *six zeroes*.

Both parts of this puzzle are complete! They provide two gold stars:
\*\*

At this point, you should [return to your Advent calendar](/2015) and
try another puzzle.