about nested namespace routes write on rail3

Question

i use

rails g scaffold_controller admin/sub/Product name:string

to generate crud page,

now i need write route.rb file to map the admin_sub_product_controller,how to write this route file on rails3?

it's hard for me to write 2 level namespace mapping route

namespace admin do
    resource :products
end

this only wokrs for /admin/products,but for mapping admin/sub/proudcts how to write?