GATE 2024 CS (CS2) – Question 62

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 ___________