Combining the data from two variables (in the same data set).

Hi everyone! How are you guys doing?

I'm fairly new on Stata and today I come here with a very simple question.

How can I combine the data from two variables (in the same data set) into one variable. I want to combine the variables in such a way that the data from one variable can replace the missing values from the other.

Here is an example of what I am looking for:



Any thoughts on how to do this? I looked for an answer exhaustively but couldn't find a solution.

Thank you in advance.