During the Summer School August 2009 the hole punch was tested that makes the square holes. The size of the badge is cells, each of which can be punched. On the diagram is a punched cell, is not punched. How many little badges will remain after using a punch?
The first line contains the sizes of the badge and . The next lines contain a diagram of the punctured badge.
Print the number of little badges that will remain after using a punch.