\--- Day 9: Stream Processing ---
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A large stream blocks your path. According to the locals, it's not safe to cross the stream at the moment because it's full of *garbage*. You look down at the stream; rather than water, you discover that it's a *stream of characters*.

You sit for a while and record part of the stream (your puzzle input). The characters represent *groups* - sequences that begin with `{` and end with `}`. Within a group, there are zero or more other things, separated by commas: either another *group* or *garbage*. Since groups can contain other groups, a `}` only closes the *most-recently-opened unclosed group* - that is, they are nestable. Your puzzle input represents a single, large group which itself contains many smaller ones.

Sometimes, instead of a group, you will find *garbage*. Garbage begins with `<` and ends with `>`. Between those angle brackets, almost any character can appear, including `{` and `}`. *Within* garbage, `<` has no special meaning.

In a futile attempt to clean up the garbage, some program has *canceled* some of the characters within it using `!`: inside garbage, *any* character that comes after `!` should be *ignored*, including `<`, `>`, and even another `!`.

You don't see any characters that deviate from these rules. Outside garbage, you only find well-formed groups, and garbage always terminates according to the rules above.

Here are some self-contained pieces of garbage:

* `<>`, empty garbage.
* `<random characters>`, garbage containing random characters.
* `<<<<>`, because the extra `<` are ignored.
* `<{!>}>`, because the first `>` is canceled.
* `<!!>`, because the second `!` is canceled, allowing the `>` to terminate the garbage.
* `<!!!>>`, because the second `!` and the first `>` are canceled.
* `<{o"i!a,<{i<a>`, which ends at the first `>`.

Here are some examples of whole streams and the number of groups they contain:

* `{}`, `1` group.
* `{{{}}}`, `3` groups.
* `{{},{}}`, also `3` groups.
* `{{{},{},{{}}}}`, `6` groups.
* `{<{},{},{{}}>}`, `1` group (which itself contains garbage).
* `{<a>,<a>,<a>,<a>}`, `1` group.
* `{{<a>},{<a>},{<a>},{<a>}}`, `5` groups.
* `{{<!>},{<!>},{<!>},{<a>}}`, `2` groups (since all but the last `>` are canceled).

Your goal is to find the total score for all groups in your input. Each group is assigned a *score* which is one more than the score of the group that immediately contains it. (The outermost group gets a score of `1`.)

* `{}`, score of `1`.
* `{{{}}}`, score of `1 + 2 + 3 = 6`.
* `{{},{}}`, score of `1 + 2 + 2 = 5`.
* `{{{},{},{{}}}}`, score of `1 + 2 + 3 + 3 + 3 + 4 = 16`.
* `{<a>,<a>,<a>,<a>}`, score of `1`.
* `{{<ab>},{<ab>},{<ab>},{<ab>}}`, score of `1 + 2 + 2 + 2 + 2 = 9`.
* `{{<!!>},{<!!>},{<!!>},{<!!>}}`, score of `1 + 2 + 2 + 2 + 2 = 9`.
* `{{<a!>},{<a!>},{<a!>},{<ab>}}`, score of `1 + 2 = 3`.

*What is the total score* for all groups in your input?

Your puzzle answer was `8337`.

\--- Part Two ---
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Now, you're ready to remove the garbage.

To prove you've removed it, you need to count all of the characters within the garbage. The leading and trailing `<` and `>` don't count, nor do any canceled characters or the `!` doing the canceling.

* `<>`, `0` characters.
* `<random characters>`, `17` characters.
* `<<<<>`, `3` characters.
* `<{!>}>`, `2` characters.
* `<!!>`, `0` characters.
* `<!!!>>`, `0` characters.
* `<{o"i!a,<{i<a>`, `10` characters.

*How many non-canceled characters are within the garbage* in your puzzle input?

Your puzzle answer was `4330`.

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

At this point, all that is left is for you to [admire your Advent calendar](/2017).

If you still want to see it, you can [get your puzzle input](9/input).