INMO 1998 Problem 3

Let $p , q, r , s$ be four integers such that $s$ is not divisible by $5$ . If there is an integer $a$ such that $pa^3 + qa^2+ ra +s$ is divisible be 5, prove that there is an integer $b$ such that $sb^3 + rb^2 + qb + p$ is also divisible by 5.