# Orchestra

## 题意翻译

- 在一个 $r \times c$ 的矩阵中有 $n$ 个点，问有多少个连续子矩阵至少包含 $k$ 个点。 - $r,c,n,k \le 10$。

## 题目描述

Paul is at the orchestra. The string section is arranged in an $r×c$ rectangular grid and is filled with violinists with the exception of $n$ violists. Paul really likes violas, so he would like to take a picture including at least $k$ of them. Paul can take a picture of any axis-parallel rectangle in the orchestra. Count the number of possible pictures that Paul can take. Two pictures are considered to be different if the coordinates of corresponding rectangles are different.

## 输入输出格式

### 输入格式

The first line of input contains four space-separated integers $r$ , $c$ , $n$ , $k$ ( $1<=r,c,n<=10$ , $1<=k<=n$ ) — the number of rows and columns of the string section, the total number of violas, and the minimum number of violas Paul would like in his photograph, respectively. The next $n$ lines each contain two integers $x_{i}$ and $y_{i}$ ( $1<=x_{i}<=r$ , $1<=y_{i}<=c$ ): the position of the $i$ -th viola. It is guaranteed that no location appears more than once in the input.

### 输出格式

Print a single integer — the number of photographs Paul can take which include at least $k$ violas.

## 输入输出样例

### 输入样例 #1

2 2 1 1
1 2


### 输出样例 #1

4


### 输入样例 #2

3 2 3 3
1 1
3 1
2 2


### 输出样例 #2

1


### 输入样例 #3

3 2 3 2
1 1
3 1
2 2


### 输出样例 #3

4


## 说明

We will use '\*' to denote violinists and '\#' to denote violists. In the first sample, the orchestra looks as follows <br></br>*#<br></br>**<br></br> Paul can take a photograph of just the viola, the $1×2$ column containing the viola, the $2×1$ row containing the viola, or the entire string section, for $4$ pictures total.In the second sample, the orchestra looks as follows <br></br>#*<br></br>*#<br></br>#*<br></br> Paul must take a photograph of the entire section.In the third sample, the orchestra looks the same as in the second sample.