The checkered field consists of white cells. The field size is
H rows and
W columns. You need to select
h rows and
w columns and fill in all the cells contained in those rows or columns. How many white cells will remain after painting?
Input
The first line contains 2 numbers:
H and
W (1 <= H, W <= 20). The second line contains 2 numbers:
h and
w (1 <= h <= H, 1 <= w <= W).
Imprint
Print the answer to the problem.
Examples
| # |
Input |
Output |
| 1 |
3 2
2 1
| 1 |
| 2 |
5 5
2 3
| 6 |
| 3 |
2 4
24 |
0 |