How to track player height distance from the ground

I am making a ground slam but I want the ground slam to only be usable when the player is at a certain height from the ground. I already created the ground slam but I am having trouble tracking the players height from the ground. I am using the third person template if that helps anyone.

This is what i have so far when it comes to tracking height.

Thank you for the help and I am sorry I did not thank you earlier. i am successfully tracking my z and it increases the higher i go and decreases the lower i go i just have two questions.

  1. The number that is displayed is always 226 when i am on the floor of course this does not change unless my z changes. I think this number is wrong however and I think i made a mistake with the way i set my code up. I am just asking if the number that should be displaying is 0 or another number instead of this number.

2.I already have my ground slam working i just want to know how would i make it available to work only if the player is a certain distance from the ground. Would i have to edit my ground slam code so that it calculates if the distance is a certain distance. For example would I have to normalize the z vector and then make a range doing this in my ground slam code?