Retrieving the number of items in the previous list

Question

I am trying to retrieve the number of items in a list and use it as the starting number in the next list.

I used the following code.

\documentclass{article}
\usepackage{enumitem}

\begin{document}
This is the first list.
\begin{enumerate}[label=M\arabic*.]
    \item item number one.
    \item item number two.
    \item item number three.
\end{enumerate}

This is the second list.

\begin{enumerate}[label=M\arabic*., start=4]
    \item item number four.
    \item item number five.
    \item item number six.
\end{enumerate}

\end{document}

How can I replace start=4 with a code such that it automatically finds the number of items in the previous list, add one to it, and finally use it as the argument of start?