Unity Extensions

i want to import a 3Ds Max 2013 file into my unity project ,what extension can i make export by it in 3Ds max to be accepted in unity ?, what extension can unity accept it to open files from other programs ?

thanks in advance

Export it as FBX. It is Native to Unity .
That or OBJ

Or 3DS. Or Collada .dae. Try them all to see which come across best, depends on the model usually.