var a:array[1..10003] of char;
    aux:char;
    nr,n,i,j,p:longint;
    f,g:text;
    ok:boolean;
begin
assign(f,'litere.in');reset(f);
assign(g,'litere.out');rewrite(g);
readln(f,n);
for i:=1 to n do
    read(f,a[i]);
nr:=0;
for i:=1 to n-1 do  begin
    p:=n;
    for j:=n downto i+1 do
        if a[j-1]>a[p] then inc(nr) else begin  aux:=a[j];
                                                a[j]:=a[p];
                                                a[p]:=aux;
                                                p:=j-1;
        end;
aux:=a[i];
a[i]:=a[p];
a[p]:=aux;
end;
writeln(g,nr);close(g);
end.