The $K_i$ of a novel competitive inhibitor designed against an enzyme is $2.5 \: \mu M$. The enzyme was assayed in the absence or presence of the inhibitor $(5 \: \mu M)$ under identical conditions. The $K_m$ in the presence of the inhibitor was found to be $30 \: \mu M$. The $K_m$ in the absence of the inhibitor is _________ $\mu M$