Min-Max Game

A and B play the following min-max game. Given the expression
N = 12 + X*(Y - Z)
where X, Y and Z are variables representing single digits (0 to 9), "A" would like to maximize N while "B" would like to minimize it. Towards this end, "A" chooses a single digit number and "B" substitutes this for a variable of her choice (X, Y or Z). "A" then chooses the next value and "B", the variable to substitute the value. Finally "A" proposes the value for the remaining variable. Assuming both play to their optimal strategies, the value of N at the end of the game would be