Const fin='litere.in';
      fout='litere.out';
Var
   f:text;
   V:Array[1..10000] of char;
   k,i,j,n:integer;
Begin
     assign(f,fin);
     reset(f);
     readln(f,n);
     for i:=1 to n do
         Read(f,V[i]);
     close(f);
     k:=0;
     for i:=1 to n-1 do
         For j:=i+1 To n do
             if V[i]>V[j] then k:=k+1;
     assign(f,fout);
     rewrite(f);
     Write(f,k);
     Close(f);
End.