how to spawn unityads every 5 time i die?

hey, i am publishing a game and to get some money from it i want ads to spawn when i collide! The game is in 2D to "OnCollisionEnter2D". I have download UnityAds from the AssetStore so please if you have a script to do this please post it here it would help me alot! (BTW the game is gonna be published on Android!) Thanks!