diff --git a/day_13.rb b/day_13.rb
new file mode 100644
index 0000000..74297f0
--- /dev/null
+++ b/day_13.rb
@@ -0,0 +1,71 @@
+regex = /(\w+) would (\w+) (\d+) happiness units by sitting next to (\w+)/
+happiness = Hash.new {|h,k| h[k] = {} }
+DATA.read.scan(regex).each do |left, sign, units, right|
+  units = units.to_i
+  units *= (sign == "gain") ? 1 : -1
+  happiness[left][right] = units
+end
+
+puts happiness.keys.permutation.map { |arrangement|
+  arrangement << arrangement.first
+  arrangement.each_cons(2).map { |left,right|
+    happiness[left][right] + happiness[right][left]
+  }.inject(:+)
+}.max
+__END__
+Alice would lose 57 happiness units by sitting next to Bob.
+Alice would lose 62 happiness units by sitting next to Carol.
+Alice would lose 75 happiness units by sitting next to David.
+Alice would gain 71 happiness units by sitting next to Eric.
+Alice would lose 22 happiness units by sitting next to Frank.
+Alice would lose 23 happiness units by sitting next to George.
+Alice would lose 76 happiness units by sitting next to Mallory.
+Bob would lose 14 happiness units by sitting next to Alice.
+Bob would gain 48 happiness units by sitting next to Carol.
+Bob would gain 89 happiness units by sitting next to David.
+Bob would gain 86 happiness units by sitting next to Eric.
+Bob would lose 2 happiness units by sitting next to Frank.
+Bob would gain 27 happiness units by sitting next to George.
+Bob would gain 19 happiness units by sitting next to Mallory.
+Carol would gain 37 happiness units by sitting next to Alice.
+Carol would gain 45 happiness units by sitting next to Bob.
+Carol would gain 24 happiness units by sitting next to David.
+Carol would gain 5 happiness units by sitting next to Eric.
+Carol would lose 68 happiness units by sitting next to Frank.
+Carol would lose 25 happiness units by sitting next to George.
+Carol would gain 30 happiness units by sitting next to Mallory.
+David would lose 51 happiness units by sitting next to Alice.
+David would gain 34 happiness units by sitting next to Bob.
+David would gain 99 happiness units by sitting next to Carol.
+David would gain 91 happiness units by sitting next to Eric.
+David would lose 38 happiness units by sitting next to Frank.
+David would gain 60 happiness units by sitting next to George.
+David would lose 63 happiness units by sitting next to Mallory.
+Eric would gain 23 happiness units by sitting next to Alice.
+Eric would lose 69 happiness units by sitting next to Bob.
+Eric would lose 33 happiness units by sitting next to Carol.
+Eric would lose 47 happiness units by sitting next to David.
+Eric would gain 75 happiness units by sitting next to Frank.
+Eric would gain 82 happiness units by sitting next to George.
+Eric would gain 13 happiness units by sitting next to Mallory.
+Frank would gain 77 happiness units by sitting next to Alice.
+Frank would gain 27 happiness units by sitting next to Bob.
+Frank would lose 87 happiness units by sitting next to Carol.
+Frank would gain 74 happiness units by sitting next to David.
+Frank would lose 41 happiness units by sitting next to Eric.
+Frank would lose 99 happiness units by sitting next to George.
+Frank would gain 26 happiness units by sitting next to Mallory.
+George would lose 63 happiness units by sitting next to Alice.
+George would lose 51 happiness units by sitting next to Bob.
+George would lose 60 happiness units by sitting next to Carol.
+George would gain 30 happiness units by sitting next to David.
+George would lose 100 happiness units by sitting next to Eric.
+George would lose 63 happiness units by sitting next to Frank.
+George would gain 57 happiness units by sitting next to Mallory.
+Mallory would lose 71 happiness units by sitting next to Alice.
+Mallory would lose 28 happiness units by sitting next to Bob.
+Mallory would lose 10 happiness units by sitting next to Carol.
+Mallory would gain 44 happiness units by sitting next to David.
+Mallory would gain 22 happiness units by sitting next to Eric.
+Mallory would gain 79 happiness units by sitting next to Frank.
+Mallory would lose 16 happiness units by sitting next to George.