9. Teacher Shi gave cards with the numbers 1, 2, 3, 4 to Jia, Yi, Bing, and Ding, respectively. Then the following conversation took place:
Jia said to Yi: Your card number is 4;
Yi said to Bing: Your card number is 3;
Bing said to Ding: Your card number is 2;
Ding said to Jia: Your card number is 1.
Teacher Shi found that: People with cards of the same parity (odd or even) always tell the truth to each other, while people with cards of different parity always lie to each other, and the sum of the numbers on Jia and Ding's cards is less than the sum of the numbers on Yi and Bing's cards.
What is the four-digit number formed by the numbers on Jia, Yi, Bing, and Ding's cards in order? $\qquad$