var a:array[1..10000] of char;
    f,g:text;
    x:char;
    nr,i,j,n:longint;
begin
     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]);
     nr:=0;
     for i:=2 to n do
     begin
          x:=a[i];  j:=i-1;
          while x<a[j] do
          begin
               a[j+1]:=a[j];
               dec(j); inc(nr);
          end;
          a[j+1]:=x;
     end;
     writeln(g,nr);
     close(g);
end.