Stack Columns From Left To Right Into One Column In Excel and the result output as to txt/csv

Dear All,

I have Excel Sheet with 2 columns (Column1 and Column2)

For Example,

Column1            Column2
A                       100
B                       150
C                       200

I would like to stack Columns From Left To Right Into One Column

Result
A
100
B
150
C
200

And the Result will be outputted to txt/csv format.

Anyone can help?