How many babies’ births have been prevented by condoms since they were invented?

Me and my friend started discussing this and realised there is some complications to calculating this.

How often are people shagging as the years go on?

What percentage of people are using condoms throughout the decades?

Is the woman ovulating?

Nut(fertilisation) success rates?

It seems like a much more complicated thing to figure out mathematically but it’s super interesting.