var
        i,z,n,t,diem:integer;
        A,B:array[1..100] of char;
begin
        readln(n);
        for i :=1 to n do
                read(A[i]);
                readln();
       diem:=0;
        for t:=1 to n do
                read(B[t]);
        for z:=1 to n do
                if (A[z]<>'.') then
                   if A[z]<>B[z] then diem:=diem+1;
        writeln(diem);
        readln
end.