2 Boxes

You have $2$ boxes, the first having $X$ stones, and the second having $Y$ stones. You want the (absolute) difference between the stones of the $2$ boxes to be exactly $K$. Each second, you can take a stone from the $1^{st}$ box and put it in the $2^{nd}$, or take from the $2^{nd}$ and put it in the $1^{st}$ box. Find the minimum time till the difference between the stones of the $2$ boxes be