4. Xiaoli put a plate of cat food in front of the big cat QiQi and the small cat TianTian. Later, Xiaoli felt that she had given too much to QiQi, so she transferred 7 pieces of cat food from QiQi's plate to TianTian's. As a result, QiQi still had 9 more pieces of cat food than TianTian. Initially, QiQi had $\qquad$ more pieces of cat food than TianTian.
$23$