KöMaL 2018 C1485

Let $x=1^2+3^2+5^2+\cdots+2017^2$ and $y=2^2+4^2+6^2+\cdots+2018^2$. Evaluate the fraction $\frac{y-x}{y+x-(1\cdot 2+2\cdot3+3\cdot4+\cdots+2017\cdot 2018)}.$