A long straight road goes from city A to city B. There are several radio stations along the road, and their ranges are described by the ints left and right. The i-th radio station can be heard at any point on the road between left[i] and right[i] kilometers from city A, inclusive.
A segment of the road is called entertaining if at least k radio stations can be heard at all points on the segment. Return the length of the longest entertaining segment of the road. If there is no such segment, return 0.