Advertising row after 4th thread in forumdisplay

[kyokushin4life]

Hi there.

I would like to have a row for advertising space after 4th thread in forumdisplay.php
eg) https://vborg.vbsupport.ru/forumdisplay.php?f=111

How could I achieve this?

Thanks all.

[BUDIMAN]

any example or screenshot ?

[kyokushin4life]

Preferably don't want to use plugin for this. Wouldl ike to achieve in template.