Consider the set of complex numbers z satisfying ∣1+z+z2∣=4. The maximum value of the imaginary part of z can be written in the form nm, where m and n are relatively prime positive integers. What is m+n?<spanclass=′latex−bold′>(A)</span>20<spanclass=′latex−bold′>(B)</span>21<spanclass=′latex−bold′>(C)</span>22<spanclass=′latex−bold′>(D)</span>23<spanclass=′latex−bold′>(E)</span>24