In reply to Vivek.

Hi Vivek,
If you want to determine the overlap length of 3 or more intervals you can just generalize the last formula in this blog, which will be this formula:

Overlap = max(0, min(A2, B2, C2, ...) - max(A1, B1, C1, ...) + 1)

where A2, B2, C2, ... are ending points (upper boundaries) of your intervals, and A1, B1, C1, ... are their beginning points (lower boundaries).