diff --git a/4/solution.nix b/4/solution.nix
index 341aa90..620ecbf 100644
--- a/4/solution.nix
+++ b/4/solution.nix
@@ -4,9 +4,7 @@ let
   # read input
   input = readFile ./input;
   pairs = let 
-    readRange = s:
-      let l = splitString "-" s;
-      in [ (toInt (head l)) (toInt (last l)) ];
+    readRange = s: split (a: b: [ (toInt a) (toInt b) ]) (splitString "-" s);
     readPair = a: b: [ (readRange a) (readRange b) ];
   in map
     (line: split readPair (splitString "," line))