Expressing distribution function of the Poisson-distribution as $F(k)=1-\int_0^{\theta}p_k(x)dx$

I am studying for an exam and got across this task, where I don't really have a clue how to do the following:

How can I express the distribution function $F(k)$ of the Poisson-distribution in this form:$F(k)=1-\int_0^{\theta}p_k(x)dx$

Poisson-distribution: $p(x)=\frac{\theta^x}{x!}e^{-\theta}, x \in \mathbb{N_0}$