Let the solution curve \( x = x(y) \), \( 0 < y \leq \frac{\pi}{2} \), of the differential equation \[ (\log_e (\cos y))^2 \cos y \, dx - (1 + 3x \log_e (\cos y)) \sin y \, dy = 0 \] satisfy \( x \left( \frac{\pi}{3} \right) = \frac{1}{2 \log_e 2} \). If \( x \left( \frac{\pi}{6} \right) = \frac{1}{\log_e m - \log_e n} \), where \( m \) and \( n \) are co-prime integers, then \( mn \) is equal to ______.