diff --git a/nhentai/__init__.py b/nhentai/__init__.py
index 14b488f..e622c47 100644
--- a/nhentai/__init__.py
+++ b/nhentai/__init__.py
@@ -1,3 +1,3 @@
-__version__ = '0.3.9'
+__version__ = '0.4.0'
 __author__ = 'RicterZ'
 __email__ = 'ricterzheng@gmail.com'
diff --git a/nhentai/utils.py b/nhentai/utils.py
index 779ce2d..caa925b 100644
--- a/nhentai/utils.py
+++ b/nhentai/utils.py
@@ -233,6 +233,9 @@ and append a file extension like '.txt', so I avoid the potential of using
 an invalid filename.
 
 """
+    return s
+
+    # maybe you can use `--format` to select a suitable filename
     valid_chars = "-_.()[] %s%s" % (string.ascii_letters, string.digits)
     filename = ''.join(c for c in s if c in valid_chars)
     if len(filename) > 100: