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+<title>Day 19 - Advent of Code</title>
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+Oh, hello! Funny seeing you here.
+
+I appreciate your enthusiasm, but you aren't going to find much down here.
+There certainly aren't clues to any of the puzzles. You do risk spoiling a few
+surprises for yourself, though. Best to play the normal way and discover
+everything as it was intended, I think. The best surprises don't even appear
+in the source until you unlock them for real.
+
+Please be careful with automated requests; I'm not Google, and I can only take
+so much traffic. Please be considerate so that everyone gets to play.
+
+If you're curious about how Advent of Code works, it's running on some custom
+Perl code. Other than a few integrations (auth, analytics, ads, social media),
+I built the whole thing myself, including the design, animations, prose, and
+all of the puzzles.
+
+The puzzles probably took the longest; the easiest ones were around 45 minutes
+each, but the harder ones took 2-3 hours, some even longer than that. A lot of
+effort went into building this thing - I hope you're enjoying playing it as
+much as I enjoyed making it for you!
+
+If you'd like to hang out, I'm @ericwastl on Twitter.
+
+- Eric Wastl
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+-->
+<body>
+<header><h1><a href="/">Advent of Code</a></h1><div class="user">Neil Smith <span class="star-count">38*</span></div><nav><ul><li><a href="/about">[About]</a></li><li><a href="/stats">[Stats]</a></li><li><a href="/leaderboard">[Leaderboard]</a></li><li><a href="/settings">[Settings]</a></li><li><a href="/auth/logout">[Log out]</a></li></ul></nav></header>
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+<main>
+<article class="day-desc"><h2>--- Day 19: Medicine for Rudolph ---</h2><p>Rudolph the Red-Nosed Reindeer is sick! His nose isn't shining very brightly, and he needs medicine.</p>
+<p>Red-Nosed Reindeer biology isn't similar to regular reindeer biology; Rudolph is going to need custom-made medicine. Unfortunately, Red-Nosed Reindeer chemistry isn't similar to regular reindeer chemistry, either.</p>
+<p>The North Pole is equipped with a Red-Nosed Reindeer nuclear fusion/fission plant, capable of constructing any Red-Nosed Reindeer molecule you need. It works by starting with some input molecule and then doing a series of <em>replacements</em>, one per step, until it has the right molecule.</p>
+<p>However, the machine has to be calibrated before it can be used. Calibration involves determining the number of molecules that can be generated in one step from a given starting point.</p>
+<p>For example, imagine a simpler machine that supports only the following replacements:</p>
+<pre><code>H => HO
+H => OH
+O => HH
+</code></pre>
+<p>Given the replacements above and starting with <code>HOH</code>, the following molecules could be generated:</p>
+<ul>
+<li><code>HOOH</code> (via <code>H => HO</code> on the first <code>H</code>).</li>
+<li><code>HOHO</code> (via <code>H => HO</code> on the second <code>H</code>).</li>
+<li><code>OHOH</code> (via <code>H => OH</code> on the first <code>H</code>).</li>
+<li><code>HOOH</code> (via <code>H => OH</code> on the second <code>H</code>).</li>
+<li><code>HHHH</code> (via <code>O => HH</code>).</li>
+</ul>
+<p>So, in the example above, there are <code>4</code> <em>distinct</em> molecules (not five, because <code>HOOH</code> appears twice) after one replacement from <code>HOH</code>. Santa's favorite molecule, <code>HOHOHO</code>, can become <code>7</code> <em>distinct</em> molecules (over nine replacements: six from <code>H</code>, and three from <code>O</code>).</p>
+<p>The machine replaces without regard for the surrounding characters. For example, given the string <code>H2O</code>, the transition <code>H => OO</code> would result in <code>OO2O</code>.</p>
+<p>Your puzzle input describes all of the possible replacements and, at the bottom, the medicine molecule for which you need to calibrate the machine. <em>How many distinct molecules can be created</em> after all the different ways you can do one replacement on the medicine molecule?</p>
+</article>
+<p>Your puzzle answer was <code>518</code>.</p><article class="day-desc"><h2>--- Part Two ---</h2><p>Now that the machine is calibrated, you're ready to begin molecule fabrication.</p>
+<p>Molecule fabrication always begins with just a single <span title="It's a Red-Nosed Reindeer electron.">electron</span>, <code>e</code>, and applying replacements one at a time, just like the ones during calibration.</p>
+<p>For example, suppose you have the following replacements:</p>
+<pre><code>e => H
+e => O
+H => HO
+H => OH
+O => HH
+</code></pre>
+<p>If you'd like to make <code>HOH</code>, you start with <code>e</code>, and then make the following replacements:</p>
+<ul>
+<li><code>e => O</code> to get <code>O</code></li>
+<li><code>O => HH</code> to get <code>HH</code></li>
+<li><code>H => OH</code> (on the second <code>H</code>) to get <code>HOH</code></li>
+</ul>
+<p>So, you could make <code>HOH</code> after <em><code>3</code> steps</em>. Santa's favorite molecule, <code>HOHOHO</code>, can be made in <em><code>6</code> steps</em>.</p>
+<p>How long will it take to make the medicine? Given the available <em>replacements</em> and the <em>medicine molecule</em> in your puzzle input, what is the <em>fewest number of steps</em> to go from <code>e</code> to the medicine molecule?</p>
+</article>
+<p>Your puzzle answer was <code>200</code>.</p><p class="day-success">Both parts of this puzzle are complete! They provide two gold stars: **</p>
+<p>At this point, you should <a href="/">return to your advent calendar</a> and try another puzzle.</p>
+<p>If you still want to see it, you can <a href="/day/19/input" target="_blank">get your puzzle input</a>.</p>
+<p>You can also <span class="share">[Share<span class="share-content">on
+ <a href="https://twitter.com/intent/tweet?text=I%27ve+completed+%22Medicine+for+Rudolph%22+%2D+Day+19+%2D+Advent+of+Code&url=http%3A%2F%2Fadventofcode%2Ecom%2Fday%2F19&related=ericwastl&hashtags=AdventOfCode" target="_blank">Twitter</a>
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+ this puzzle.</p>
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