>>> from resistor import resistor

>>> resistor('22-6489/4_97*ABC')
3
>>> resistor('21-AS*DF/3')
1
>>> resistor('21-AS*DF/X')
0
>>> resistor('ABC-FF*3-897/D')
2
>>> resistor('ABC-FF*N-A97')
0
>>> resistor('A/123/45*67-8*99-456/2_864')
8
>>> resistor('A/B123/C45*77-8*99-H456/2_864')
5