@string = qw(34, 56, 78, 90, 98, 76, 54, 32, 10, 12, 13, 16, 19, 20, 10, 56);

sub nth_iter {
	my($item, $n, @list) = @_;
	$i = -1;
	$match = 0;
	$len = @list;
	while ($i++ < $len) {
		if($list[$i] == $item) {
			$match++;
			if ($match == $n) {
				last;
			}
		}
	}
	if ($match != $n) {
		$i = -1;
	}
	return $i;
}
        
print nth_iter(78, 1, @string);