Saw my first roach in my apartment, should I be worried?

Hi, all I've just had a roach in my apartment. I live in a studio apartment, so only one big room, on the ground floor. I have been living here for 2 months and it is the first one I have seen, but it was small and I read somewhere that the small ones were the ones you should worry about.

The thing is I haven't seen any before this one and I have for the first time today had the window open for an extended period of time.

So my question is: Should I be worried, as it was, presumably, a German roach or do you think it could just be a one off, because of the open window?

Edit added info: It was on the wall next to the window, or at least that was where I saw it first, but the window had been closed for a while at that point.