Program Litere;
Var
 n, i: Integer; ci: LongInt; orc, j: Byte;
 s: array[1..10000] of Char;
 o: array[1..26] of Integer;
 f, g: Text;
 c: Char;
BEGIN
 Assign(f,'litere.in'); Reset(f);
 ci:=0;
 ReadLn(f,n);
 For i:=1 to n do
  Begin
   Read(f,c);
   orc:=Ord(c)-96;
   {WriteLn(c,' - ',orc:2,' ....... ci = ',ci:2);}
   Inc(o[orc]);
   For j:=orc+1 to 26 do
    Inc(ci,o[j]);
  End;
 Assign(g,'litere.out'); ReWrite(g);
 Write(g,ci);
 Close(g);
 Close(f);
END.