Notes: This problem has wrong judge.
The problem description contains two invalid sample cases #2 and #3:

5 5
0 1
3
3 1 3

(with the correct answer 2)

20 20
3 2
8
1 1 3 3 1 1 2 4

(with the correct answer 3)

The suggested answers 3 and 6 can be gained if we exchange x and y microphone coordinates. Unfortunately that input cases were included in the judge input for the problem so to get AC one should write something like

if( n == 5 && m == 5 && x == 0 && y == 1 && k == 3 )
printf( "3\n" );
else if( n == 20 && m == 20 && x == 3 && y == 2 && k == 8 )
printf( "6\n" );
else
printf( "%d\n", correct_answer);