var f1,f2:text;
    i,n,nr,x,j,f,gs:longint;
    ok:boolean;
    c:array[1..10010] of char;
    v:array[1..10010] of longint;
begin
        assign(f1,'litere.in');
        reset(f1);
        assign(f2,'litere.out');
        rewrite(f2);
        readln(f1,n);
        for i:=1 to n do
                read(f1,c[i]);
        x:=n;
        for j:=26 downto 1 do
        begin
                nr:=0;
                for i:=1 to n do
                begin
                        if ord(c[i])-96=j then
                                inc(nr);
                        if ord(c[i])-96<j then
                                v[i]:=v[i]+nr;
                end;
        end;
        nr:=0;
        for i:=1 to n do
                inc(nr,v[i]);
        writeln(f2,nr);
        close(f1);
        close(f2);
end.