program litere;
type litere1=array[1..10000]of char;
var a:litere1;
		i,j,z,n:integer;
		aux:char;
		f,g:text;
begin
	 z:=0;
	 assign(f,'litere.in');
	 reset(f);
	 assign(g,'litere.out');
	 rewrite(g);
	 readln(f,n);
	 for i:=1 to n do read(f,a[i]);
	 for i:=1 to n do
		 for j:=1 to n-1 do
			 if a[j]>a[j+1] then  begin
															 aux:=a[j];
															 a[j]:=a[j+1];
															 a[j+1]:=aux;
															 z:=z+1;
														end;
	write(g,z);
	close(f);
	close(g);
end.