0.
As others have said, mine has to be a one and done. It seems like most failures come from half hearted attempts or poor planning, or backing out at the last minute.
No matter what method I use, I will be employing a plastic bag over my head for insurance that survival is 0%.
If I had access to benzos or something, I would just OD on those. They wouldn't make me ctb on their own, and they don't need to. The plastic bag will take care of the heavy lifting once I lose consciousness, so there will be no waking up in the hospital or something like that.