Solution (source code)

= Solution

Put $Y_n=n(1-M_n)\geq0$. For fixed $x\geq0$ and sufficiently large $n>x$,
$$
\mathbb P(Y_n>x)=\mathbb P(M_n<1-x/n)=(1-x/n)^n\longrightarrow e^{-x}.
$$
For $x<0$ its distribution function is zero. The limiting distribution function is therefore $F(x)=0$ for $x<0$, $F(x)=1-e^{-x}$ for $x\geq0$, the <exponential distribution> of rate one. Since this distribution function is continuous everywhere,
$$
\boxed{n(1-M_n)\ \xrightarrow{d}\ \operatorname{Exp}(1).}
$$