calculus - How to prove that $sum_{1}^{infty} frac{1}{n^3} le 1.5$

I have this sequence:
$$\sum_{1}^{\infty} \frac{1}{n^3}$$

and I need to prove that: $\sum_{1}^{\infty} \frac{1}{n^3} \le 1.5$

So basically I know that this sequence converges using the integral test, but I don't know how to prove the above statement.

Some help?