var f,g:text;
    n,i,k,l,aux:integer;
    j:char;
    a:array[1..10000]of char;
    fv:array['a'..'z'] of byte;
begin
     assign(f,'litere.in'); reset(f);
     assign(g,'litere.out'); rewrite(g);
     readln(f,n);
     l:=0;
     for i:=1 to n do
         begin
         read(f,a[i]);
         inc(fv[a[i]]);
         if i>1 then begin aux:=i-1;
                           while aux>0 do
                                 begin
                                 if a[aux]>a[i] then inc(l);
                                 aux:=aux-1;
                                 end;
                     end
         end;
     writeln(g,l);
     close(f); close(g);
end.