Q20

Let $\text{S}$ be the set of all ternary strings defined over the alphabet $\{a, b, c\}$. Consider all strings in $\text{S}$ that contain at least one occurrence of two consecutive symbols, that is, $\text{"aa"}$, $\text{"bb"}$ or $\text{"cc"}$. The number of such strings of length $5$ that are possible is __________. (Answer in integer).