GATE CSE 2024 Session 2 Q62: Strings of length at most 4 in b*ab*(ab*ab*)*

Let $L_1$ be the language represented by the regular expression $b^*ab^*(ab^*ab^*)^*$ and $L_2 = \{w \in (a + b)^* \mid |w| \le 4\}$, where $|w|$ denotes the length of string $w$. The number of strings in $L_2$ which are also in $L_1$ is ___________