MAGICJAR (1502) Don't understand the problem

Hi,what I understand of this problem is that: for a valid J, their exist a valid combination of junior chefs that haven’t finished yet their dishes, and the sum of their nb of ingredients equals to J.Then those junior chefs are erased from the list of chefs.
I don’t understand the editorial, that tells in short that the answer is sum(A) - N + 1.
Let’s choose an example: 4 junior chefs whose number of ingredients are 3,3,3 and 9. We can choose J=9, and finish in 2 steps: 3+3+3 and 9. The answer of the editorial is 3+3+3+9 - 4 + 1 = 15. I don’t know how 15 leads to a solution, as if we choose 3+3+9 and 3, in the second step, 3 is different that 15.
Could you please tell me how to understand the subject?
Thanks in advance.