A $PI$ controller with integral time constant of $0.1$ min is to be designed to control a process with transfer function
$$G_{P}\left ( s \right )=\frac{10}{s^{2}+2s+100}$$
Assume the transfer functions of the measuring element and the final control element are both unity $\left ( G_{m} =1,G_{f}=1\right )$. The gain (rounded off to the first decimal place) of the controller that will constitute the critical condition for stability of the $PI$ feedback control system is _____________