diff --git a/index.en.html b/index.en.html
index 637b03028a4c2e3bf774199d8ee4289dd8cde0f6..cbfb7757cee223d335a67ec368ec03a2ea3d1f55 100644
--- a/index.en.html
+++ b/index.en.html
@@ -142,7 +142,7 @@
                 </div>
             </div>
             <div class="col">
-                <iframe src="./fit_a_line/index.en.html" style="border: none; overflow-y : hidden" width="100%" height="100%" name="content_iframe" id="content_iframe">
+                <iframe src="./01.fit_a_line/index.en.html" style="border: none; overflow-y : hidden" width="100%" height="100%" name="content_iframe" id="content_iframe">
                 </iframe>
             </div>
         </div>
diff --git a/index.html b/index.html
index d1bc2ca0e16985ab63b965770cf001b16eb7fbf3..9cc744529ec35fe5dcb356bd1fcb3a2bd354762c 100644
--- a/index.html
+++ b/index.html
@@ -146,7 +146,7 @@
                 </div>
             </div>
             <div class="col">
-                <iframe src="./fit_a_line/index.html" style="border: none; overflow-y : hidden" width="100%" height="100%" name="content_iframe" id="content_iframe">
+                <iframe src="./01.fit_a_line/index.html" style="border: none; overflow-y : hidden" width="100%" height="100%" name="content_iframe" id="content_iframe">
                 </iframe>
             </div>
         </div>
diff --git a/index.html.tmpl b/index.html.tmpl
index 0dcd6342af32de6b515f04f1706eeffd625aabfd..3729ec62426c393c08afb934fcfc2d61832cfcd3 100644
--- a/index.html.tmpl
+++ b/index.html.tmpl
@@ -118,7 +118,7 @@
                 </div>
             </div>
             <div class="col">
-                <iframe src="./fit_a_line/index{% if is_en %}.en{% endif %}.html" style="border: none; overflow-y : hidden" width="100%" height="100%" name="content_iframe" id="content_iframe">
+                <iframe src="./01.fit_a_line/index{% if is_en %}.en{% endif %}.html" style="border: none; overflow-y : hidden" width="100%" height="100%" name="content_iframe" id="content_iframe">
                 </iframe>
             </div>
         </div>