Total from NBT tags

Hey I'm trying to figure out how to subtract a total from NBT tags. I'm doing a repair system where you right click on something and it takes out 1 plank for each stage of damage. sometimes it takes 3 planks. it'd be easy enough if it was just one plank type but sometimes the player will have 2 oak and maybe 1 spruce plank.. i'm not great with loops but thats the path i been trying to go down. kind of the only way that really seems to make it work.. any ideas??