How to combine two columns (with missing data)?

[#1]

got a table with missing data like this:

Column1	Column2
1	•
•	5
•	7
3	•

Need to combine it it to one column

Column3

1

5

7

3

I used sum but it didn't work. The only way I can do is using If and is Missing() formual. Any fast way to combine it? 

Thanks!

[#2]

OK. I figured out. I need to use sum() instead of +.