Number can not keep consistant

[hsymoon]

Hi ,
I have 3regions. Regins1:A1-B1, regions2:A2-B2 , regionsC:A1-B2( which is the overlap of region 1&2).I think region3_reads_number=region1_reads_number+region2_reads_number. But it is not.My results are followd:

[hsymoon]

Here is bed file used：

Thank you so much for helping me