Given a set of N axis aligned rectangles, you need to find the area of their union. Each rectangle is represented by two points, one lower-left point and one upper-right point. The coordinates are all integers.

Input:
First line consists of N denoting the number of rectangles.
Following N lines consist of $x1$,$y1$,$x2$,$y2$ each where $(x1,y1)$ represents the lower-left point and $(x2,y2)$ represents the upper-right point of i th rectangle.

Output:
Print the area of the union of the rectangles.

Constraints:
$1 \le N \le 10^4$
$1 \le x1$ < $x2 \le 10^5$
$1 \le y1$ < $y2 \le 10^5$