diff --git a/day18-scratch.lisp b/day18-scratch.lisp
index 02b7cca..0096129 100644
--- a/day18-scratch.lisp
+++ b/day18-scratch.lisp
@@ -105,3 +105,58 @@
 
 (defparameter *day-18-input-connectivity*
   (make-array (find-maxes *day-18-input-coords*) :initial-element 0))
+(fill-connectivity-array *day-18-input-coords* *day-18-input-connectivity*)
+
+(count-open-sides *day-18-input-connectivity*)
+
+;; now. how could i only include surface area
+;; did i need to model points as what?
+;;
+;; well, i could start with 0th layer. there's no stone there, only air
+;; and start filling with 2
+;; then count for all points as previously, but only neighbors which are 2
+;; i guess
+
+;; so. start at '(0 0 0)
+;; then get neighbors, filter those that are 0
+;; put into queue / list - actually dfs is good enough, so just recurse?
+
+(point-at-is '(0 0 0) *day-18-test-graph-connectivity* 0)
+(point-at-is '(0 0 0) *day-18-test-graph-connectivity* 2)
+
+(fill-outside-with-2 '(0 0 0) *day-18-test-graph-connectivity*)
+;; this seems to work.
+;; now i want to cound only outside that contacts 2?
+;; so, same cound but look for neighbors 2 and count them, not 6 - stone-neighbors
+
+(count-open-sides-to-outside *day-18-test-graph-connectivity*)
+;; well, now i need to add 1 to all sides
+
+(setq *day-18-test-input*
+      (coords-from-input "day18-test.txt"))
+
+(setq *day-18-test-graph-connectivity*
+ (make-array (find-maxes *day-18-test-input*) :initial-element 0))
+(fill-connectivity-array *day-18-test-input* *day-18-test-graph-connectivity*)
+
+(fill-outside-with-2 '(0 0 0) *day-18-test-graph-connectivity*)
+(count-open-sides-to-outside *day-18-test-graph-connectivity*)
+;; and now it's 58
+;; so, let's cound for full input?
+
+;;; part 2
+
+(setq *day-18-input-coords*
+      (coords-from-input "day18-input.txt"))
+
+(setq *day-18-input-connectivity*
+  (make-array (find-maxes *day-18-input-coords*) :initial-element 0))
+(fill-connectivity-array *day-18-input-coords* *day-18-input-connectivity*)
+
+(fill-outside-with-2 '(0 0 0) *day-18-input-connectivity*)
+(count-open-sides-to-outside *day-18-input-connectivity*)
+;; there's 1 at the edge of the array. whoops. so there are 0s in the input?
+;; yep. so now what, shift all by 1? and add one more +1 to the find max?
+;; hahaha, this is stupid.
+
+;; but let's do it
diff --git a/day18.lisp b/day18.lisp
index e0700c7..60ee43b 100644
--- a/day18.lisp
+++ b/day18.lisp
@@ -11,9 +11,9 @@
 (defun find-maxes (all-coords)
  (loop
   for (x y z) in all-coords
-  maximize (1+ x) into xs
-  maximize (1+ y) into ys
-  maximize (1+ z) into zs
+  maximize (+ x 2) into xs
+  maximize (+ y 2) into ys
+  maximize (+ z 2) into zs
   finally (return (list xs ys zs))) )
 
 (defun fill-connectivity-array (all-coords connectivity-matrix)
@@ -21,7 +21,8 @@
     for (x y z) in all-coords
     do (setf (aref connectivity-matrix x y z) 1)))
 
-(defun neighbors-for (coords connectivity-matrix)
+;; 1 - rock, 0 - initial empty, 2 - outside air
+(defun neighbors-for (coords connectivity-matrix &key (type 1))
   (labels ((coords-fit (potential-point)
              (loop for i from 0 to 2
                    always (and (< (nth i potential-point)
@@ -34,7 +35,7 @@
       for neighbor = (mapcar #'+ coords deltas)
       when
       (and (coords-fit neighbor)
-           (= 1 (apply #'aref connectivity-matrix neighbor)))
+           (= type (apply #'aref connectivity-matrix neighbor)))
       collect neighbor)))
 
 (defun count-open-sides (connectivity-matrix)
@@ -46,3 +47,25 @@
                       when (= 1 (aref connectivity-matrix x y z))
                       summing (- 6
                       (length (neighbors-for (list x y z) connectivity-matrix))))))))
+
+(defun point-at-is (coords connectivity-matrix elem)
+  (= elem (apply #'aref connectivity-matrix coords)))
+
+;; call with initial coord '(0 0 0)
+(defun fill-outside-with-2 (coord connectivity-matrix)
+  (when (point-at-is coord connectivity-matrix 0)
+    (setf (apply #'aref connectivity-matrix coord) 2)
+    (mapcar (lambda (neighbor) (fill-outside-with-2 neighbor connectivity-matrix))
+            (neighbors-for coord connectivity-matrix :type 0))))
+
+(defun count-open-sides-to-outside (connectivity-matrix)
+  (destructuring-bind (n m k)
+      (array-dimensions connectivity-matrix)
+    (loop for x from 0 below n sum
+          (loop for y from 0 below m sum
+                (loop for z from 0 below k
+                      when (= 1 (aref connectivity-matrix x y z))
+                      summing (length (neighbors-for
+                                       (list x y z)
+                                       connectivity-matrix
+                                       :type 2)))))))