Fewer*

https://www.merriam-webster.com/dictionary/less

The traditional view is that less applies to matters of degree, value, or amount and modifies collective nouns, mass nouns, or nouns denoting an abstract whole while fewer applies to matters of number and modifies plural nouns. Less has been used to modify plural nouns since the days of King Alfred and the usage, though roundly decried, appears to be increasing.