Proof Writing & Problem Solving · Easy problem

Suppose, for contradiction, that $\sqrt{3} = \dfrac{p}{q}$ in lowest terms. Then $p^2 = 3q^2$, so $3 \mid p$; write $p = 3m$. Substituting gives $q^2 = c\,m^2$ for a whole number $c$. What is $c$?