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.
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*<sub class="lower-index">*i*</sub> and *y*<sub class="lower-index">*i*</sub> (1 ≤ *x*<sub class="lower-index">*i*</sub> ≤ *r*, 1 ≤ *y*<sub class="lower-index">*i*</sub> ≤ *c*): the position of the *i*-th viola. It is guaranteed that no location appears more than once in the input.
We will use '*' to denote violinists and '#' to denote violists.

In the first sample, the orchestra looks as follows 

In the second sample, the orchestra looks as follows 

In the third sample, the orchestra looks the same as in the second sample.
2 2 1 1
1 2
4
3 2 3 3
1 1
3 1
2 2
1
3 2 3 2
1 1
3 1
2 2
4
1 1 1 1
1 1
1
10 10 10 10
6 1
3 8
10 6
10 3
10 4
8 9
2 3
5 7
5 9
5 1
4
10 10 10 1
8 2
9 10
6 8
10 7
1 8
4 4
6 3
2 3
8 8
7 2
2073
5 9 2 2
4 6
1 5
40
6 4 10 2
2 3
2 1
1 2
6 1
1 4
4 4
2 4
1 1
6 3
4 2
103
8 2 4 4
3 2
3 1
2 2
7 1
4
2 6 2 2
1 2
1 5
8
7 5 3 1
5 5
4 5
1 4
135
10 10 10 6
3 4
10 9
6 5
4 9
2 10
10 10
9 8
8 2
5 6
1 5
78
10 10 10 4
5 7
9 7
5 8
3 7
8 9
6 10
3 2
10 8
4 1
8 10
414
10 10 10 1
8 10
2 9
1 10
3 1
8 5
10 1
4 10
10 2
5 3
9 3
1787
10 10 10 3
2 7
6 3
10 2
2 4
7 8
1 2
3 1
7 6
6 8
9 7
751
10 10 10 2
4 4
1 7
10 5
2 8
5 5
6 9
7 3
9 5
5 3
6 6
1416
10 10 10 10
8 2
1 4
9 9
5 2
1 7
1 5
3 10
6 9
7 8
3 3
4
10 10 10 10
1 9
5 2
5 1
8 5
9 10
10 2
5 4
4 3
3 6
1 5
1
10 10 10 10
5 6
4 4
8 9
5 7
9 2
6 4
7 3
6 10
10 3
3 8
6
10 10 10 1
9 3
7 5
8 2
3 8
1 6
3 9
7 3
10 4
5 3
1 3
1987
10 10 10 1
1 10
10 8
7 4
7 2
1 3
6 6
10 1
2 7
9 3
3 10
1991
10 10 10 1
4 5
9 6
3 6
6 10
5 2
1 7
4 9
10 8
8 1
2 9
2082
r, c, n, k = map(int, input().split())

board = [[0 for col in range(c)] for row in range(r)]
for i in range(n):
    x, y = map(lambda x: int(x)-1, input().split())
    board[x][y] = 1

photos = 0
for x1 in range(r):
    for y1 in range(c):
        for x2 in range(x1, r):
            for y2 in range(y1, c):
                s = 0
                for row in range(x1, x2+1):
                    s += sum(board[row][y1:y2+1])
                if s >= k:
                    photos += 1

print(photos)
