The Cloud Firewall service doesn't allow you to block requests from a specific country. You can allow an IP range, though unless you're 100% sure that your country/ISP owns all IP's in all four ranges, by allowing access from each, you may be allowing access from a country other than your own.
Honestly, the best way to go about limiting access would be per IP. Since you have a dynamic IP, the way around this would be to setup and connect to a VPN. The VPN would provide a static IP and that would be the IP allowed to access SSH.
This would be the best route as it's far easier to manage a whitelist then it is a large blacklist. It's better to simply blacklist everyone other than what you whitelist, which is what most recommend when setting up a firewall.