program ex;
type
 ss=array[1..500]of char;
var
 a,b,c:ss;
 f1,f2:text;
 n:integer;
procedure init;
 var
  i,j,m:integer;
 begin
  assign(f1,'palin.in');
  assign(f2,'palin.out');
  reset(f1);
  rewrite(f2);
  readln(f1,n);
  for i:=1 to n do
   read(f1,a[i]);
  m:=n;
  n:=n div 2;
  for i:=1 to n do
   b[i]:=a[i];
  i:=0;
  if (m mod 2<>0) then inc(n);
  for j:=m downto n+1 do
   begin
    inc(i);
    c[i]:=a[j];
   end;
 end;
procedure main;
 var
  i,t:integer;
 begin
  t:=0;
  for i:=1 to n do
   if b[i]<>c[i] then
     t:=t+2;
  writeln(f2,t);
 end;
begin
 init;
 main;
 close(f2);
end.