diff --git a/interfaces/demo1.go b/interfaces/demo1.go
index 7bdc511..bd77184 100644
--- a/interfaces/demo1.go
+++ b/interfaces/demo1.go
@@ -35,4 +35,8 @@ func Demo1()  {
 	}
 
 	school(r)
+
+	c:= circle{radius: 10}
+
+	school(c)
 }
\ No newline at end of file