var     f,g:text;
        v:array[1..10000] of integer;
        c:array[1..10000] of char;
        i,m,nr,s,n:integer;
        j:char;
begin
assign (f,'litere.in');reset (f);
assign (g,'litere.out');rewrite (g);
readln (f,n);
for i:=1 to n do begin
 read (f,c[i]);
 v[i]:=i;
end;
nr:=1;
for j:='a' to 'z' do begin
 m:=0;
 for i:=1 to n do
  if c[i]=j then begin
   s:=s+v[i]-nr;
   inc(nr);
  end;
 for i:=n downto 1 do begin
  v[i]:=v[i]+m;
  if c[i]=j then inc(m);
 end;
end;
writeln (g,s);
close(f);close(g);
end.