Merging multiple column data to new column !!

Hi,

Thanks in advance for your support.

I have an input file as follows

DA1 BAL1 DA2 BAL2 DA3 BAL3
1 100 3 300 4 400
2 200 1 400 6 600

The output need to be as,

DA BAL
1 100
2 200
3 300
1 400
4 400
6 600

Can you please throw a light on this ? I am trying with row normalizer and d-normalizer but no results as of now.