$$
\begin{align}
[\text{Prog}] &\to [\text{Func}] \\
[\text{Func}] &\to
\begin{cases}
\text{identefier} \\
\text{[statement]}
\end{cases}
\\
[\text{statement}] &\to
\begin{cases}
\text {return} \\
\text{[expr]}
\end{cases} \\
[\text{expr}] &\to
\text{int}
\end{align}
$$