Banner in under first message

[Ricsca]

I would like to insert Google banners in my forum. I saw that there is an advertising section with many options but they all seem invasive to me.
I would like the banners to appear under the first message and after x replies.
How can I do it?
Thank you
Banner in under first message

free plugins
minecraft paid for free
mcmarket
mc-market
free minecraft paid plugins
free minecraft plugins
spigotmc
SpigotMC
aac free
ewg free
Minecraft Premium Plugins
ewg free download
litebans free
epicworldgenerator free
free schematics
leaked schematics minecraft
schematics
schematics leaked
schematics free
minecraft schematics free
paid minecraft schematics free
paid minecraft schematics for free
free cracked plugins
free cracked minecraft plugins
plugins
featherboard download
featherboard plugin download
antiaura download
xenforo leaked
xenforo for free
xenforo addons