$ABC$ is a triangle with $AB = 33$, $AC = 21$, and $BC = m$, where $m$ is an integer. There are points $D$ and $E$ on sides $AB$ and $AC$ respectively such that $AD = DE = EC = n$, where $n$ is also an integer. Find the value of $m$.

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