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+--- Day 13: Shuttle Search ---
+
+Your ferry can make it safely to a nearby port, but it won't get much further. When you call to book
+another ship, you discover that no ships embark from that port to your vacation island. You'll need
+to get from the port to the nearest airport.
+
+Fortunately, a shuttle bus service is available to bring you from the sea port to the airport!  Each
+bus has an ID number that also indicates how often the bus leaves for the airport.
+
+Bus schedules are defined based on a timestamp that measures the number of
+minutes since some fixed reference point in the past. At timestamp 0, every bus simultaneously
+departed from the sea port. After that, each bus travels to the airport, then various other
+locations, and finally returns to the sea port to repeat its journey forever.
+
+The time this loop takes a particular bus is also its ID number: the bus with ID 5 departs from the
+sea port at timestamps 0, 5, 10, 15, and so on. The bus with ID 11 departs at 0, 11, 22, 33, and so
+on. If you are there when the bus departs, you can ride that bus to the airport!
+
+Your notes (your puzzle input) consist of two lines.  The first line is your estimate of the
+earliest timestamp you could depart on a bus. The second line lists the bus IDs that
+are in service according to the shuttle company; entries that show x must be out of service, so you
+decide to ignore them.
+
+To save time once you arrive, your goal is to figure out the earliest bus you can take to
+the airport. (There will be exactly one such bus.)
+
+For example, suppose you have the following notes:
+
+939
+7,13,x,x,59,x,31,19
+
+Here, the earliest timestamp you could depart is 939, and the bus IDs in service are 7, 13, 59, 31,
+and 19. Near timestamp 939, these bus IDs depart at the times marked D:
+
+time   bus 7   bus 13  bus 59  bus 31  bus 19
+929      .       .       .       .       .
+930      .       .       .       D       .
+931      D       .       .       .       D
+932      .       .       .       .       .
+933      .       .       .       .       .
+934      .       .       .       .       .
+935      .       .       .       .       .
+936      .       D       .       .       .
+937      .       .       .       .       .
+938      D       .       .       .       .
+939      .       .       .       .       .
+940      .       .       .       .       .
+941      .       .       .       .       .
+942      .       .       .       .       .
+943      .       .       .       .       .
+944      .       .       D       .       .
+945      D       .       .       .       .
+946      .       .       .       .       .
+947      .       .       .       .       .
+948      .       .       .       .       .
+949      .       D       .       .       .
+
+The earliest bus you could take is bus ID 59. It doesn't depart until timestamp 944, so you would
+need to wait 944 - 939 = 5 minutes before it departs. Multiplying the bus ID by the number of
+minutes you'd need to wait gives 295.
+
+What is the ID of the earliest bus you can take to the airport multiplied by the number of
+minutes you'll need to wait for that bus?
+
+