PE-MO 2015 Problem 3

Let $a_1, a_2, . . . , a_n$ be positive integers, with $n \ge 2$ , such that $$\lfloor \sqrt{a_1 \cdot a_2\cdot\cdot\cdot a_n} \rfloor = \lfloor \sqrt{a_1} \rfloor \cdot \lfloor \sqrt{a_2} \rfloor \cdot\cdot\cdot \lfloor \sqrt{a_n} \rfloor.$$ Prove that at least $n - 1$ of these numbers are perfect squares.

Clarification: Given a real number $x$ , $\lfloor x\rfloor$ denotes the largest integer that is less than or equal to $x$ . For example $\lfloor \sqrt2\rfloor$ and $\lfloor 3\rfloor =3$ .