A bag contains \( 4 \frac{2}{3} \) dozens of candies, out of which \( a \) are lemon candies. If one candy is drawn at random from the bag, there is some probability that it will be a lemon candy. Now, \( 4 \frac{2}{3} \) dozen more lemon candies are put in the bag, and the probability of drawing a lemon candy will be \( 2 \frac{1}{2} \) times higher than in the first case. Find \( a \).