Call a positive integer \(n\) \(k\)-pretty if \(n\) has exactly \(k\) positive divisors and \(n\) is divisible by \(k\). For example, \(18\) is \(6\)-pretty. Let \(S\) be the sum of positive integers less than \(2019\) that are \(20\)-pretty. Find \(\tfrac{S}{20}\).