diff --git a/2017/ruby/day_13.rb b/2017/ruby/day_13.rb
index 6ec1ff7..1af2f4a 100644
--- a/2017/ruby/day_13.rb
+++ b/2017/ruby/day_13.rb
@@ -1,62 +1,11 @@
-input = ARGF.read.strip
-# input = <<INPUT
-# 0: 3
-# 1: 2
-# 4: 4
-# 6: 4
-# INPUT
-@input = Hash[input.scan(/(\d+): (\d+)/).map {|x| x.map(&:to_i) }]
-
-class Firewall
-  def initialize(input)
-    @layers = input
-    @scanners = Hash[input.map {|d,_| [d, 0] }]
-    @deltas = Hash[input.map {|d,_| [d, 1] }]
-  end
-
-  def each
-    return enum_for(__method__) unless block_given?
-
-    loop do
-      yield @scanners
-
-      @layers.each do |depth, range|
-        @scanners[depth] += @deltas[depth]
-        @deltas[depth] = case @scanners[depth]
-                         when 0
-                           1
-                         when range - 1
-                           -1
-                         else
-                           @deltas[depth]
-                         end
-      end
-    end
-  end
+firewall = Hash[ARGF.read.strip.scan(/(\d+): (\d+)/).map {|x| x.map(&:to_i) }]
 
+def caught?(time, range)
+  (time % (2 * (range - 1))).zero?
 end
 
-def pass?(delay)
-  f = Firewall.new(@input).each
-  delay.times do
-    f.next
-  end
+p firewall.select {|depth, range| caught?(depth, range) }.map {|d,r| d * r }.sum
 
-  severity = 0
-  (0..@input.map(&:first).max).each do |pos|
-    scanners = f.next
-    return false if scanners[pos] == 0
-  end
-  true
-end
-
-def s(t, r)
-  r - (t % (2*r) - r).abs
-end
-
-(0..Float::INFINITY).each do |delay|
-  if @input.all? {|d,r| s(d + delay, r-1) != 0 }
-    p delay
-    exit
-  end
-end
+p (1..Float::INFINITY).find {|delay|
+  firewall.none? {|depth, range| caught?(delay+depth, range) }
+}