Given $n$ rectangles, your task is to determine the total area of their union.

The first line has an integer $n$ : the number of rectangles.

After that, there are $n$ lines describing the rectangles. Each line has four integers $x_1$ , $y_1$ , $x_2$ and $y_2$ : a rectangle begins at point $(x_1,y_1)$ and ends at point $(x_2,y_2)$ .

• $1 \le n \le 10^5$
• $-10^6 \le x_1 < x_2 \le 10^6$
• $-10^6 \le y_1 < y_2 \le 10^6$

Print the total area covered by the rectangles.