How many csections is considered "safe"?

I know your chances of complication go up with each delivery, but I'm wondering how many is "too" many?

I've had three csections so far.. 2014, 2016, year and a half ago, I'm pregnant with #4 due in September, obviously I am going to have to do another C-section. I'm just wondering if I should get my tubes tied or if a fifth baby might be a possibility.