diff --git a/day17.cr b/day17.cr
new file mode 100644
index 0000000..12c97f9
--- /dev/null
+++ b/day17.cr
@@ -0,0 +1,46 @@
+require "advent"
+INPUT = input(2020, 17).lines.map(&.chars) 
+
+def part1(input)
+  step = input.clone
+  cubes = Set({Int32,Int32,Int32,Int32}).new
+  new_cubes = Set({Int32,Int32,Int32,Int32}).new
+  input.each_with_index do |row, y|
+    row.each_with_index do |c, x|
+      cubes << {x,y,0,0} if c == '#'
+    end
+  end
+
+  6.times do |i|
+    neighbor_count = {} of {Int32,Int32,Int32,Int32} => Int32
+    cubes.each do |c|
+      x,y,z,w = c
+      (-1..1).each do |dx|
+        (-1..1).each do |dy|
+          (-1..1).each do |dz|
+            (-1..1).each do |dw|
+              next if dx == 0 && dy == 0 && dz == 0 && dw == 0
+              neighbor_count[{x+dx,y+dy,z+dz,w+dw}] = (neighbor_count[{x+dx,y+dy,z+dz,w+dw}]? || 0) + 1
+            end
+          end
+        end
+      end
+    end
+    new_cubes.clear
+    neighbor_count.each do |n, i|
+      if cubes.includes?(n)
+        new_cubes << n if (i == 2 || i == 3)
+      elsif i == 3
+        new_cubes << n
+      end
+    end
+    new_cubes, cubes = cubes, new_cubes
+  end
+  cubes.size
+end
+
+def part2(input)
+end
+
+puts part1(INPUT.clone)
+puts part2(INPUT.clone)