Let $D, E, F$ be points on the sides $BC, CA, AB$ of a triangle $ABC$, respectively. Suppose $AD, BE, CF$ are concurrent at $P$. If $\frac{PF}{PC} = \frac{2}{3}$, $\frac{PE}{PB} = \frac{2}{7}$ and $\frac{PD}{PA} = \frac{m}{n}$, where $m, n$ are positive integers with $\gcd(m, n) = 1$, find $m + n$.

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