var f,g:text;
    a:array[1..10000] of char;
    nr,i,n,j:longint;
    x:char;
begin
assign(f,'litere.in');reset(f);
assign(g,'litere.out');rewrite(g);
readln(f,n);
nr:=0;
for i:=1 to n do begin
    read(f,a[i]);
    x:=a[i];
    for j:=1 to i-1 do
        if x<a[j] then inc(nr);
    end;
write(g,nr);
close(f);
close(g);
end.