Let \( a_n = \dfrac{b_{n+1}}{b_n} \), where \( b_1 = 1 \), \( b_2 = 1 \), and \( b_{n+2} = b_n + b_{n+1} \), \( n \in \mathbb{N} \). Then \( \lim_{n \to \infty} a_n \) is