How can I keep a fixed public IP in Amazon EC2?

I'm hosting a Minecraft server on an Amazon EC2 instance.

Every time I reboot the instance, it has a new public and private IP.

How can I keep the same public IP? Private IP doesn't concern me.

You can't, unless you pay for a static IP from your provider/host server.

Amazon EC2 allows access to Amazon Cloud Computing services but does not guarantee continuous service availability. The service is a distributed service and when you connect, you may be reaching a different server with a different IP address from the one you used previously.

EC2 is not intended as a website hosting service. To host a server, you need to find a website hosting service, which EC2 is not.