A system with transfer function ^{$ \left[ \begin{array} \ Y(s) \\ X(s) \end{array} \right] $} = ^{$\dfrac{s}{s+p}$}has an output y(t) = cos ^{$ \left( \begin{array} \ 2t - \dfrac{\pi}{3} \end{array} \right) $}for the input signal x(t) = p cos ^{$ \left( \begin{array} \ 2t - \dfrac{\pi}{2} \end{array} \right) $}. Then, the system parameter ‘p’ is