In a sequence of independent trials, let $E_n$ be the event that a success occurs on the $n$-th trial, with $P(E_n) = p$. A random variable $K$ is defined as the number of trials until the first success. Given that the first success occurs after the 3rd trial ($K > 3$), what is the probability that the first success occurs on the 6th trial ($K = 6$)?