A number $m$ is randomly selected from the set $\{11,13,15,17,19\}$, and a number $n$ is randomly selected from $\{1999,2000,2001,\cdots,2018\}$. Find the probability that $m^n$ has a units digit of $1$. Express your answer in the form of a fraction \frac{k}{l} in simplest form, and provide the value of k + l.

Let's think step by step and output the final answer within \boxed{}.
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