Given a list of steps and an additional step, determine where the step fits into the original list of steps. A correct answer, correctly places the given step into the set of steps so that it creates a new plausible set of steps. Output must be formatted as 'After step n', where n is the step number after which the given additional step is to be inserted.

Steps: (1) The flu virus has receptors, which are like viral Velcro, on the surface of the virus particle (2) The receptors will lock onto a target cell using these chemical receptors on the surface, which docks onto the cell surface (3) The receptors  then go into the cell (4) The receptors take it over and make it produce thousands or in some cases millions of copies of new viruses (5) The copies come streaming out of the cell (6) The copies infect other cells to make more viruses, or they escape from the body and infect a new victim  
Where does the following step fit into the given list of steps: The receptors use it like a factory 
 After step 3. 