diff --git a/05-hydrothermal-venture/code.scm b/05-hydrothermal-venture/code.scm
index 52e486d..04ae979 100644
--- a/05-hydrothermal-venture/code.scm
+++ b/05-hydrothermal-venture/code.scm
@@ -1,8 +1,5 @@
 (import (srfi :43)) ; vector extensions
-
-; returns numbers 0 to 9 from ascii character
-(define (char->number c)
-  (- (char->integer c) 48)) ; 48 is ASCII's number zero
+(load "../common.scm")
 
 ; reads a numnber from input
 ; also consumes the next non-number character in the file!