var
m,n,i,j,k,s,l:integer;
A: array [1..15000] of LongInt;
B: array [1..1000000] of LongInt;

begin
s:=0;
readln(n);
        for i:=1 to n do readln(A[i]);
readln(m);
        for j:=1 to m do begin readln(B[j]);     end;
i :=  1;
j :=  n;
k := 1;
for l:=1 to m do
        begin
                while  (i <=j) do
                begin
                k := (i + j) div 2;
                if B[l] > A[k] then i := k + 1
                                else j := k -1;

                end;
                if A[k] = B[l]  then s:=s+1;



        end;


writeln();
writeln(s);
readln;
end.

Try this test:
3
10
11
12
3
12
11
10

thanks

result must be 3 or no :)

In your program teacher's dates should not be the same.
But once you will fix this your program won't pass test 8 because of time limit.
You have to use binary search. And in binary search there can be the same teacher's dates.