What is the minimum number of equivalents of $\mathrm{NaNH}{}_2$ needed in liquid ammonia to convert 1,2-dibromopropane completely into sodium propynide, $\mathrm{CH}{}_3-\mathrm{C}\equiv \mathrm{C}{}^{-}\mathrm{Na}{}^{+}$?

Two equivalents bring about the two successive dehydrobrominations ($\mathrm{CH}{}_3\mathrm{CHBrCH}{}_2\mathrm{Br}$ to a bromopropene to propyne). The terminal alkyne is then acidic enough to be deprotonated by a third equivalent. Total = 3.