Selecting Numbers based on Complex Criteria

[Deks]

Sorry for making such confusion. I'm a newbie and needs help to write the formula to arrive at the sum presented in C1. I only know the simplest form like C1 = sum(a1+b1)

RULE #1
If A1 = 0, 1, 7, or 8 and B1 = any number, then C1 = 0
If A1 = 2 and B1 = any number, then C1 =1
If A1 = 3 and B1 = 0, 1, or 2, then C1 = 2
If A1 = 4 and B1 = 0, 1, or 2, then C1 = 3
If A1 = 3 or 4 and B1 = 3, then C1 = 4

RULE #2
If A1 = 0, 1, 2, 7, or 8 and B1 = 0, 1, or 8, then C1 = 0
If A1 = 0, 1, 2, 7, or 8 and B1 = 2 or 3, then C1 = 2
If A1 = 3 or 4 and B1 = 0 or 1, then C1 = 2
If A1 = 3 and B1 = 2 or 3 , then C1 = 3
If A1 = 4 and B1 = 2 or 3, then C1 = 4

Any number is 0, 1, 2, 3, 8 (no 4, 5, 6, or 7)

Thanks in advance!