sub adv_tr {
  my ($str, $x, $from, $to) = @_;
  my $pos = -1;
  ($pos = index($str, $from, $pos + 1)) == -1 and return $str while $x--;
  eval "substr(\$str, $pos) =~ tr/\Q$from\E/\Q$to\E/";
  $str;
}