Let \( f^1(x) = \frac{3x + 2}{2x + 3}, \; x \in \mathbb{R} - \left\{ \frac{-3}{2} \right\} \). For \( n \ge 2 \), define \( f^n(x) = f^1 \circ f^{n-1}(x) \). If \( f^5(x) = \frac{ax + b}{bx + a} \), \( \gcd(a,b) = 1 \), then \( a + b \) is equal to _______.
