Program p1;
var fi,fo : text;
    i,k,j,n :longint;  t:boolean;
    a : array[1..10000] of char;
    c : array[1..10000] of integer;
begin
    assign(fi,'litere.in'); reset(fi);  readln(fi,n);
    assign(fo,'litere.out'); rewrite(fo);
    read(fi,a[1]);  k:=0; c[1]:=0;

    for i:=2 to n do begin
                     read(fi,a[i]);
                     j:=i-1; t:=true; c[i]:=0;
                     while (j>0) and (t=true) do begin
                               if a[j]>a[i] then c[i]:=c[i]+1
                                            else if a[i]=a[j] then begin
                                                                   c[i]:=c[i]+c[j];
                                                                   t:=false;
                                                                   end;
                                                 j:=j-1;
                                                 end;
                     end;
    for i:=1 to n do k:=k+c[i];
    write(fo,k);
    close(fi); close(fo);
end.