reshaping pandas dataframe tanking columns ' as rows '

Question

I need to reshape a dataframe like that:

A	B	X	Y
a1	b1	x1	y1
a2	b2	x2	y2

to

A	B	Columns1	result
a1	b1	X	x1
a2	b2	X	x2
a1	b1	Y	y1
a2	b2	Y	y2

is there an easy way? I need to avoid an output with pandas multi-index.

Thanks for the suggestions