I'm developing an idle RPG and it will be released on google play in several days. It's about hero battles on other planets. The story revolves around an energy stone called Valorium and the battles between DarkScepter and Valorian to take the stone.

I want to run ads for my game in the first period to increase the number of downloads but I can't choose which countries should I target. I found that the US, Russia, South Korea, Australia, and Canada might be good choices.

Do you guys have any advice or suggest?