Problem Statement

Yu-T is hunting for treasure on a grid of $H\times W$ cells.

Each cell is represented by coordinates $(r, c) (1 \leq r \leq H, 1 \leq c \leq W)$. Here, $r$ is the row number counted from the top, and $c$ is the column number counted from the left.

Yu-T has obtained $N$ pieces of information in advance. The $i$-th piece of information indicates that there is no treasure in the rectangular region specified by the upper-left cell $(r_{1,i}, c_{1,i})$ and the lower-right cell $(r_{2,i}, c_{2,i})$.

Based on all the information, find the number of cells that may contain treasure.

Constraints

• All inputs are integers
• $1 \leq H, W \leq 2000$
• $1 \leq N \leq 2\times 10^5$
• $1 \leq r_{1,i} \leq r_{2,i} \leq H$
• $1 \leq c_{1,i} \leq c_{2,i} \leq W$

Input

$H$ $W$ $N$
$r_{1, 1}$ $c_{1, 1}$ $r_{2, 1}$ $c_{2, 1}$ 
$r_{1, 2}$ $c_{1, 2}$ $r_{2, 2}$ $c_{2, 2}$ 
$\vdots$
$r_{1, N}$ $c_{1, N}$ $r_{2, N}$ $c_{2, N}$ 

Output

Output the number of cells that may contain treasure.

Print a newline at the end.

Sample

4 4 2
1 1 3 2
1 2 1 4

8

....      xx..      xxxx
....  ->  xx..  ->  xx..
....      xx..      xx..
....      ....      ....

3 3 3
1 1 3 1
1 2 3 2
1 3 3 3

0

...      x..      xx.      xxx
...  ->  x..  ->  xx.  ->  xxx
...      x..      xx.      xxx

9 9 1
5 5 5 5

80

.........    .........
.........    .........
.........    .........
.........    .........
......... -> ....#....
.........    .........
.........    .........
.........    .........
.........    .........