Repeat what the Mu'adh-dhin says, except for when he says:
Hayya 'alas-Salāh (hasten to the prayer) and Hayya 'alal-Falāh (hasten to salvation). Here you should say:
Lā ḥawla wa lā quwwata 'illā billāh.
There is no might and no power except by Allah.
Reference:
Al-Bukhari 1/152, Muslim 1/288.