var a:array['a'..'z'] of longint;
    s:array[1..10001] of char;
    f,g:text;
    i,n,nr:longint;
    c:char;
begin
 assign(f,'litere.in'); reset(f);
 assign(g,'litere.out'); rewrite(g);
 readln(f,n);
 for i:=1 to n do
  read(f,s[i]);
 nr:=0;
 inc(a[s[i]]);
 for i:=n-1 downto 1 do begin
  nr:=nr-a[s[i]];
  for c:=s[i] downto 'a' do
   inc(nr,a[c]);
  inc(a[s[i]]);
 end;
 writeln(g,nr);
 close(f); close(g);
end.