$19$ points For any string win${}^{**}$ and symbol ain$,$ let $n_a(w)$ denote

the number of times a appears in $w.($We will be using this notation

regularly this semester.$)$

Construct a regular expression describing the following language over

the alphabet $\{0,1\}$

$L=\{w|n_0(w)-=1,$mod$3\}.$

Hint: First try constructing a regular expression accepting all strings

with $w$ with $n_0(w)$ is divisible by $3.$