# Pastebin ac3E1Adg
diff --git a/app.pl b/app.pl
--- a/app.pl
+++ b/app.pl
@@ -8,12 +8,18 @@ get '(*dir)/:file' => sub {
     my $self = shift;
     my $dir  = $self->param('dir');
     my $file = $self->param('file');
+    unless (-f "html/$dir/$file.html") {
+        return $self->render(template => 'does_not_exist');
+    }
     return $self->redirect_to("/$dir/$file.html");
 };

 get '(*dir)/' => sub {
     my $self = shift;
     my $dir  = $self->param('dir');
+    unless (-d "html/$dir") {
+        return $self->render(template => 'does_not_exist');
+    }
     return $self->redirect_to("/$dir.html");
 };