--- a/app.py
+++ b/app.py
@@ -1,2 +1,6 @@
 def shipping(region, total):
+    if region not in {'local', 'remote'}:
+        raise ValueError('unknown region')
+    if region == 'local' and total >= 100:
+        return 0
     return 8 if region == 'local' else 15