Given a set of rectangles {R₁, R₂, · · · , R_n}, compute the area of their common intersection. i.e.,</p>

Area (R₁ ∩ R₂ ∩ · · · ∩ R_n)

The edges of the rectangles R₁, R₂, · · · , R_n, are either vertical or horizontal lines.

For example, the intersection of 4 rectangles, R₁, R₂, R₃, and R₄, in the following figure is the shaded rectangle.

입력 형식

T.IN 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:</p>

x1 x2 y1 y2

such that 0 ≤ x₁ < x₂ ≤ 10,000 and 0 ≤ y₁ < y₂ ≤ 10,000, and x₁, x₂, y₁ and y₂ are int

출력 형식

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

예제 입력 1

2
0 2 0 2
1 3 1 3

예제 출력 1

1

예제 입력 2

3
1 4 1 8
0 2 0 5
10 15 22 35

예제 출력 2

0