By floor function, there are $\lfloor \frac{2018}{18} \rfloor=112$ positive integers less than 2019 that divisible by 18 and $\lfloor \frac{2018}{21} \rfloor=96$ positive integers less than 2019 that divisible by 21 If a number is divisible by both 18 and 21, then it is divisible by $lcm(21,18)=126$, so there are $\lfloor \frac{2018}{126} \rfloor=16$ positive integers less than 2019 that divisible by both 18 and 21. By PIE, there are $112+96-16=192$ positive integers that divisible by either 18 or 21