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Problem Statement

There are $N$ rectangular sheets spread out on a coordinate plane.

Each side of the rectangular region covered by each sheet is parallel to the $x$- or $y$-axis. Specifically, the $i$-th sheet covers exactly the region satisfying $A_i \le x \le B_i$ and $C_i \le y \le D_i$.

Let $S$ be the area of ​the region covered by one or more sheets​. It can be proved that $S$ is an integer under the constraints. Print $S$ as an integer.

Constraints

• $2 \le N \le 100$
• $0 \le A_i < B_i \le 100$
• $0 \le C_i < D_i \le 100$
• All input values are integers.

Input

The input is given from Standard Input in the following format:

Output

Print the area $S$ of the region covered by one or more sheets as an integer.

3
0 5 1 3
1 4 0 5
2 5 2 4

20

The three sheets cover the following regions. Here, red, yellow, and blue represent the regions covered by the first, second, and third sheets, respectively.

Therefore, the area of the region covered by one or more sheets is $S=20$.

2
0 100 0 100
0 100 0 100

10000

Note that different sheets may cover the same region.

3
0 1 0 1
0 3 0 5
5 10 0 10

65