How do Multiple columns into one long column?

Would someone have any idea how to do this? (It keeps re-occuring in my work and copy/paste is getting old.
I have many more columns than the example.

FROM:
1, 2
3, 4
5, 6

TO
1
3
5
2
4
6

NOT
1
2
3
4
5
6

thanks,
crzzy1