Let the circles $\mathrm{C}_1:|z|=\mathrm{r}$ and $\mathrm{C}_2:|z-3-4 \mathbf{i}|=5, z \in \mathbb{C}$, be such that $\mathrm{C}_2$ lies within $\mathrm{C}_1$. If $z_1$ moves on $\mathrm{C}_1, z_2$ moves on $\mathrm{C}_2$ and $\min \left|z_1-z_2\right|=2$, then $\max \left|z_1-z_2\right|$ is equal to: