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+# Day1: The Tyranny of the Rocket Equation
+
+## Problem
+
+### Part One
+
+Santa has become stranded at the edge of the Solar System while delivering
+presents to other planets! To accurately calculate his position in space,
+safely align his warp drive, and return to Earth in time to save Christmas, he
+needs you to bring him measurements from fifty stars.
+
+Collect stars by solving puzzles. Two puzzles will be made available on each
+day in the Advent calendar; the second puzzle is unlocked when you complete the
+first. Each puzzle grants one star. Good luck!
+
+The Elves quickly load you into a spacecraft and prepare to launch.
+
+At the first Go / No Go poll, every Elf is Go until the Fuel Counter-Upper.
+They haven't determined the amount of fuel required yet.
+
+Fuel required to launch a given module is based on its mass. Specifically, to
+find the fuel required for a module, take its mass, divide by three, round
+down, and subtract 2.
+
+For example:
+
+* For a mass of 12, divide by 3 and round down to get 4, then subtract 2 to
+get 2.
+* For a mass of 14, dividing by 3 and rounding down still yields 4, so
+the fuel required is also 2.
+* For a mass of 1969, the fuel required is 654.
+* For a mass of 100756, the fuel required is 33583.
+
+The Fuel Counter-Upper needs to know the total fuel requirement. To find it,
+individually calculate the fuel needed for the mass of each module (your puzzle
+input), then add together all the fuel values.
+
+What is the sum of the fuel requirements for all of the modules on your
+spacecraft?
+
+### Part Two
+
+During the second Go / No Go poll, the Elf in charge of the Rocket Equation
+Double-Checker stops the launch sequence. Apparently, you forgot to include
+additional fuel for the fuel you just added.
+
+Fuel itself requires fuel just like a module - take its mass, divide by three,
+round down, and subtract 2. However, that fuel also requires fuel, and that
+fuel requires fuel, and so on. Any mass that would require negative fuel should
+instead be treated as if it requires zero fuel; the remaining mass, if any, is
+instead handled by wishing really hard, which has no mass and is outside the
+scope of this calculation.
+
+So, for each module mass, calculate its fuel and add it to the total. Then,
+treat the fuel amount you just calculated as the input mass and repeat the
+process, continuing until a fuel requirement is zero or negative. For example:
+
+* A module of mass 14 requires 2 fuel. This fuel requires no further fuel (2
+	divided by 3 and rounded down is 0, which would call for a negative fuel), so
+	the total fuel required is still just 2.
+* At first, a module of mass 1969
+	requires 654 fuel. Then, this fuel requires 216 more fuel (654 / 3 - 2). 216
+	then requires 70 more fuel, which requires 21 fuel, which requires 5 fuel,
+	which requires no further fuel. So, the total fuel required for a module of
+	mass 1969 is 654 + 216 + 70 + 21 + 5 = 966.
+* The fuel required by a module of mass 100756 and its fuel is: 33583 + 11192 +
+	3728 + 1240 + 411 + 135 + 43 + 12 + 2 = 50346.
+
+What is the sum of the fuel requirements for all of the modules on your
+spacecraft when also taking into account the mass of the added fuel? (Calculate
+the fuel requirements for each module separately, then add them all up at the
+end.)