diff --git a/03b.lisp b/03b.lisp
new file mode 100644
index 0000000..c9cab7b
--- /dev/null
+++ b/03b.lisp
@@ -0,0 +1,40 @@
+(require :uiop)
+(load (sb-ext:posix-getenv "ASDF"))
+(asdf:load-system 'cl-heap)
+
+(defun bank-max-joltage-step (known-buffer unknown-buffer depth)
+  ;; (format t "~A:~A~%" known-buffer unknown-buffer)
+  (if (= (length known-buffer) depth)
+    (parse-integer known-buffer)
+    (loop for i from 0 to (- (length unknown-buffer) (- depth (length known-buffer)))
+      collect
+      (let* (
+            (digit (subseq unknown-buffer i (+ i 1)))
+            (new-unknown-buffer (subseq unknown-buffer (+ i 1)))
+            (new-known-buffer (format nil "~A~A" known-buffer digit)))
+        (list (- 0 (parse-integer new-known-buffer)) new-known-buffer new-unknown-buffer depth)))))
+(bank-max-joltage-step "" "234234234234278" 2)
+
+(defun bank-max-joltage (bank depth)
+  (defparameter *queue* (make-instance 'cl-heap:priority-queue))
+  (cl-heap:enqueue *queue* (list "" bank depth) 0)
+  (loop
+    do (defparameter *candidate* (apply #'bank-max-joltage-step (cl-heap:dequeue *queue*)))
+    when (integerp *candidate*)
+    do (return *candidate*)
+    do (loop for branch in (reverse *candidate*)
+             do (cl-heap:enqueue *queue* (cdr branch) (car branch)))
+    )
+  )
+(bank-max-joltage "234234234234278" 2)
+(bank-max-joltage "234234234234278" 12)
+
+(defun bank-max-joltage12 (bank)
+  (bank-max-joltage bank 12)
+  )
+(defun array-total-joltage (bank-list depth)
+  (reduce #'+
+    (mapcar #'bank-max-joltage12 bank-list)))
+
+(array-total-joltage (uiop:read-file-lines "03example.txt") 12)
+(array-total-joltage (uiop:read-file-lines "03data.txt") 12)
diff --git a/flake.nix b/flake.nix
index a47cafa..079157b 100644
--- a/flake.nix
+++ b/flake.nix
@@ -23,7 +23,7 @@
         default = pkgs.mkShellNoCC {
           packages = with pkgs; [
             shellcheck
-            (sbcl.withPackages (ps: [ps.str]))
+            (sbcl.withPackages (ps: [ps.str ps.cl-heap]))
           ];
         };
       }