var n,nr,i,j:integer;
    f:text;
    a:array[1..10000] of char;
begin
assign(f,'litere.in');reset(f);
readln(f,n);
read(f,a[1]);
nr:=0;
for i:=2 to n do begin
                 read(f,a[i]);
                 for j:=1 to i-1 do if a[i]<a[j] then inc(nr);
                 end;
close(f);
assign(f,'litere.out');rewrite(f);
write(f,nr);
close(f);
end.