not sure what should be SHARED or PRIVATE in openmp loop

I have a loop which updates a matrix A and I want to make it openmp but I'm not sure what variables should be shared and private. I would have thought just ii and jj would work but it doesn't. I think I need an !$OMP ATOMIC UPDATE somewhere too...

The loop just calculates the distance between N and N-1 particles and updates a matrix A.

            !$OMP PARALLEL DO PRIVATE(ii,jj)
            do ii=1,N-1
                    do jj=ii+1,N
                            distance_vector=X(ii,:)-X(jj,:)
                            distance2=sum(distance_vector*distance_vector)
                            distance=DSQRT(distance2)
                            coff=distance*distance*distance
                            PE=PE-M(II)*M(JJ)/distance
                            A(jj,:)=A(jj,:)+(M(ii)/coff)*(distance_vector)
                            A(ii,:)=A(ii,:)-(M(jj)/coff)*(distance_vector)
                    end do
            end do
            !$OMP END PARALLEL DO