The perpendicular bisector of a line segment with end points $\left(\mathrm{1,2},6\right)$ and $\left(-\mathrm{3,6},2\right)$ passes through $\left(-\mathrm{6,2},4\right)$ and has the equation of the form $\frac{x+6}{l}=\frac{y-2}{m}=\frac{z-4}{n}$ (Where $l,m,n$ are integers, $l$ is a prime number and $l>0$), then the value of $lmn-\left(l+m+n\right)$ equals to