Node.JS express compile less in different folder

I need to compile *.less files in different folder inside public directory. I've git this dir structure:

/public:
  /stylesheets:
    /less:
       style.less
    /css:
       style.css
  /js
  /img
  ...

In my app configure function I've got following:

app.use(require('less-middleware')({
  src: '/less',
  dest: '/css',
  root: path.join(process.cwd(), 'public/stylesheets')
}));

app.use(express["static"](path.join(process.cwd(), 'public')));

But It does't work. Less files never compiles in css folder. Whats wrong?

PS: I could access to the less folder via path: /stylesheets/less/style.less. But why? Why not just /less/style.less? Thanks for any help!