To determine the half life of a radioactive element, a student plots a graph of \(\ln \left | \dfrac{dN(t)}{dt} \right |~\text {versus t. Here}\dfrac {dN(t)}{dt}\) is the rate of radioactive decay at time t. If the number of radioactive nuclei of this element decreases by
a factor of p after 4.16 years, the value of p is