diff --git a/2022/ruby/day_25.rb b/2022/ruby/day_25.rb
new file mode 100644
index 0000000..1927981
--- /dev/null
+++ b/2022/ruby/day_25.rb
@@ -0,0 +1,29 @@
+places = (0..).lazy.map { 5 ** _1 }
+digits = { ?- => -1, ?= => -2 }
+
+sum = ARGF.read.lines(chomp: true)
+  .map {|snafu|
+    snafu.reverse.chars
+      .map { digits.fetch(_1, _1.to_i) }
+      .zip(places)
+      .map { _1 * _2 }
+      .sum
+  }.sum
+
+n_places = places.slice_after { 2*_1 >= sum }.take(1).to_a.flatten.reverse
+
+require "z3"
+
+solver = Z3::Solver.new
+
+n_places.each do |place|
+  solver.assert Z3.Int(place.to_s) <= 2
+  solver.assert Z3.Int(place.to_s) >= -2
+end
+solver.assert n_places.map { _1 * Z3.Int(_1.to_s) }.sum == sum
+
+fail unless solver.satisfiable?
+p n_places
+  .map { solver.model[Z3.Int(_1.to_s)].to_i }
+  .map { digits.invert.fetch(_1, _1) }
+  .join