diff --git a/src/advent/util.cr b/src/advent/util.cr
index e7337ae..bd82cfb 100644
--- a/src/advent/util.cr
+++ b/src/advent/util.cr
@@ -49,3 +49,10 @@ struct Tuple(*T)
     { self[0]//gcd, self[1]//gcd}
   end
 end
+
+struct Number
+  def signum
+    return 0 if self == 0
+    self // self.abs
+  end
+end