im trying to figure out an if statement for our counter tops, this is what it is now

=IF(Field_Joint_Qty>0,Field_Joint_1_Location,Width)

but lets say i want to deduct from the answer of above with,

IF(Left_Finish_End>0,-M!Base_Side_Finished_End_Thickness)

i can't seem to figure out how to write this one

thank you