--- Ex.10.java	2007-05-29 20:15:19.000000000 +0100
+++ Ex.11.java	2007-05-29 20:16:06.000000000 +0100
@@ -31,6 +31,7 @@
     for (i = 0; i < r.length; ++i) s+=r[i];
     System.out.println("" + s + " bottles of beer on the wall");
     //@ assert r.length == pubs.length;
+    //@ assert s >= 0;
     return i + 1 + s;
   }
 }