Let's assume router's ether1 interface will be used for WAN. And let's assume ether1 is
not member of any bridge. So the minimum config would be this:
/interface vlan
add name=wan interface=ether1 vlan-id=180
/ip address
add address=81.244.55.234/30 interface=wan
/ip route
add dst-address=198.198.2.0/23 gateway=81.244.55.233
Not sure why ISP would be instructing you to use specific IP address as gateway for specific remote subnet ... as the public IP address given to you with netmask means the only other host IP address available in WAN subnet is the IP address of
that gateway ... but you would really want to use it as default gateway, hence
/ip route
add dst-address=0.0.0.0/0 gateway=81.244.55.233
instead of the one I wrote in the first config excerpt.