AT_abc449_f [ABC449F] Grid Clipping

There is a grid with $ H $ rows and $ W $ columns. The cell at the $ r $ -th row from the top and $ c $ -th column from the left is called cell $ (r,c) $ . Each cell is painted black or white: cell $ (R_k,C_k) $ is black for $ k=1,2,\ldots,N $ , and the remaining $ HW-N $ cells are white. Find the number of rectangular regions in this grid with $ h $ rows and $ w $ columns such that all cells contained in them are painted white. More formally, find the number of pairs of integers $ (r_0, c_0) $ satisfying all of the following conditions: - $ 1\le r_0 \le H-h+1 $ - $ 1\le c_0 \le W-w+1 $ - Cell $ (r_0+i,c_0+j) $ is painted white for all pairs of integers $ (i,j) $ satisfying $ 0\le i< h,\ 0\le j< w $ .

The input is given from Standard Input in the following format: > $ H $ $ W $ $ h $ $ w $ $ N $ $ R_1 $ $ C_1 $ $ R_2 $ $ C_2 $ $ \vdots $ $ R_N $ $ C_N $

Output the answer.

### Sample Explanation 1 The two rectangular regions enclosed in red in the figure below satisfy all the conditions.  ### Sample Explanation 2 No rectangular region satisfies all the conditions. ### Constraints - $ 1\le h\le H\le 10^9 $ - $ 1\le w\le W\le 10^9 $ - $ 0\le N\le 2\times 10^5 $ - $ 1\le R_k\le H $ - $ 1\le C_k\le W $ - $ (R_{k_1},C_{k_1}) \neq (R_{k_2},C_{k_2}) $ $ (k_1 \neq k_2) $ - All input values are integers.