Devise a two$-$bits counter with inputs $"$up$"$ and "down" $($in addition to the common clock$)$ using

two JK flip$-$llops. A third SR flip$-$flop stores whether or not the counter should currently be

counting $"$up$"$ or "down"; the $"$up$"$ input makes the clock start counting $"$up$"$ and the "down" input

makes the clock start counting "down".