Approximately how many stars are there in the sky

We have over one billion galaxies in the universe.
In our milky way, we have around 300 billion stars. 
Astronomers don't know for sure how many stars there are, considering the universe goes on and on and on (etc)
But did you know, there are more stars than every grain of sand here on earth?!

the creation of oxygen

Explanation: i just took the k12 test :)