The fifth question: If an infinite sequence of positive real numbers $\left\{x_{n}\right\}$ satisfies: $x_{0}=1, x_{i} \geq x_{i+1}(i \in N)$, then the sequence is called a “good sequence”. Find the smallest constant $c$ such that there exists a “good sequence” $\left\{x_{n}\right\}$ satisfying: $\sum_{i=0}^{n} \frac{x_{i}^{2}}{x_{i+1}} \leq c$ for any positive integer $n$.