Ok, lets start from beginning. Subnet /28 is 16 addresses. The one with low numbers is 0-15, where for simple use with whole subnet on one interface, .0 and .15 are "wasted" for network address and broadcast. There are two basic ways how you can get /28:
1) Routed subnet. It means that on ISP side would be only route to 184.108.40.206/28 via 220.127.116.11 and whole subnet would be yours. You could split it any way you want and route any address anywhere you need it in your network. And it would be possible to use all 16 of them.
2) Other subnet on WAN. ISP would assign 139.1.2.x/28 (one address) to their router. The rest minus network address and broadcast would be yours (so 13 addresses) and you'd be expected to have all hosts in /28 reachable on your WAN interface.
If you say you can use .1 - .14, I can't decide what you have. Probably 1) and maybe they just expected that you put it on internal interface and end up with 14 useable addresses (including the one on router).
In any case, if you already have some other addresses from /28 on router, you'll want to route just a single address to server. You can:
a) Give server only 18.104.22.168 and no other address. On router:
add dst-address=22.214.171.124/32 gateway=<name of internal interface with connected server>
On server (using RouterOS syntax; but the same can be done on other systems too, it's called point to point addressing):
add address=126.96.36.199/32 interface=<server's wan> network=10.100.100.3 comment="RouterOS puts remote address in network field"
add dst-address=0.0.0.0/0 gateway=10.100.100.3
b) Let server have internal address (probably 10.100.100.x) and also 188.8.131.52. On router:
add dst-address=184.108.40.206/32 gateway=<server's internal ip address>
On server, in addition to internal address:
add address=220.127.116.11/32 interface=<loopback or other interface>
In this case, if you'd want to use 18.104.22.168 for outgoing connections, you'd have to configure programs to specifically bind to this address.
If you don't get lost in it and set it up correctly (or if I didn't make some stupid mistake), the following can happen:
a) It will work.
b) It won't work because the way you get /28 is in fact option 2). Then it would require proxy ARP on router:
add address=22.214.171.124 interface=<WAN> published=yes