Given a set of rectangles { R1, R2, ... Rn }, compute the area of their common intersection i.e. :
Area( $ R1 \cap  R2  \cap R3  .... \cap Rn $ } 
The edges of the rectangle R1, R2, ... Rn  are either vertical or horizontal lines
For example, the intersection of the 4 rectangles in the following example is the shaded rectangle:

The first line specifies the number of rectangles n, where 1 < n < 1,000. Since the sides of the rectangles are parallel to the x and y axes, each rectangle is bounded by the lines x = x1, x = x2, y = y1 and y = y2 and each subsequent line of the input thus specifies one rectangle in the following format: x1 x2 y1 y2 such that 0 <= x1 < x2 <= 10,000 and 0 <= y1 < y2 <= 10,000 and x1, x2, y1, y2 are all integers. 

The output file contains the area of the intersection of all the rectangles.

NOI