CN-TST 2016 Problem 13

Let $n$ be an integer greater than $1$ , $\alpha$ is a real, $0<\alpha < 2$ , $a_1,\ldots ,a_n,c_1,\ldots ,c_n$ are all positive numbers. For $y>0$ , let $$f(y)=\left(\sum_{a_i\le y} c_ia_i^2\right)^{\frac{1}{2}}+\left(\sum_{a_i>y} c_ia_i^{\alpha} \right)^{\frac{1}{\alpha}}.$$ If positive number $x$ satisfies $x\ge f(y)$ (for some $y$ ), prove that $f(x)\le 8^{\frac{1}{\alpha}}\cdot x$ .