program litere;
var f,g:Text;
    v:array[0..30]of 0..10000;
    n,i,j:integer;
    cont:longint;
    x,max:{array[1..10000]of} char;
begin
assign(f,'litere.in');
assign(g,'litere.out');
reset(f);
rewrite(g);
readln(f,n);
cont:=0;
max:='a';
for i:=1 to n do
  begin
    read(f,x);

    {if (v[ord(x[i])-ord('a')]>1)then
      begin
        for j:=i-1 downto 1 do
          if (x[j]>x[i])then cont:=cont+1;
      end;}

    for j:=ord(x)-ord('a')+1 to ord(max)-ord('a') do
      cont:=cont+v[j];
    if (x>max) then max:=x;
    v[ord(x)-ord('a')]:=v[ord(x)-ord('a')]+1;
  end;
write(g,cont);
writeln;
close(f);
close(g);
end.