18
0S -> S0
1S -> S1
C0 -> 0C
C1 -> 1C
0C -> D
1C -> E
S1 -> SBC
S0 -> SAC
FA -> AF
FB -> BF
GA -> AG
GB -> BG
SA -> SF
SB -> SG
0 -> S0
1 -> S0
FD -> _
GE -> _