def get_overlap(a, b):
	""" return the len of overlap between two regions """
	q_start = int(a[0])
	q_end = int(a[1])
	r_start = int(b[0])
	r_end = int(b[1])

	if q_start == q_end:
		q_end += 1 		# otherwise it doesnt work for SNPs

	ret = max(0, min(q_end, r_end) - max(q_start, r_start))
	return(ret)