Can the present be absent?

Calculus Level 4

$\mathscr{E} = \displaystyle \int_{0}^{\infty} \dfrac{x^{2015}}{(1+x)^{2017}} \, dx$

If $\mathscr{E}$ can be represented in the form $\dfrac{a}{b}$ , with $a, b$ being positive coprime integers, find $a + b$ .