14. It can be solved as a math problem. First, find the least common multiple of 4 and 6, that is, 12, then there are at least 12 masks, and if two are born, two will be added, that is 14. This question applies to the knowledge of the least common multiple. The common multiple of two or more integers is called their common multiple, and the smallest common multiple except 0 is called the smallest common multiple of these integers.