Expressjs Challenge: STYLISH CSS exercise: Result Didn't Match Expected

I have only one result which doesn’t match the expected one:
<pre>Cannot GET /main.css</pre>" != "<pre>Error: EACCES: permission denied, open &#39;/home/mintkem/Desktop/expressworks/exercises/stylish_css/public/main.css&#39;</pre>

And here’s my code:
var express = require('express'); var app = express(); app.use(require('stylus').middleware(__dirname + '/public')); app.use(express.static(process.argv[3]||path.join(__dirname, 'public'))); app.listen(process.argv[2]);