CF14B.Young Photographer

Among other things, Bob is keen on photography. Especially he likes to take pictures of sportsmen. That was the reason why he placed himself in position $x_{0}$ of a long straight racetrack and got ready to take pictures. But the problem was that not all the runners passed him. The total amount of sportsmen, training at that racetrack, equals $n$ . And each of them regularly runs distances within a particular segment of the racetrack, which is the same for each sportsman. For example, the first sportsman runs from position $a_{1}$ to position $b_{1}$ , the second — from $a_{2}$ to $b_{2}$

What is the minimum distance that Bob should move to have a chance to take pictures of each sportsman? Bob can take a picture of a sportsman, if he stands within the segment that this sportsman covers on the racetrack.

The first line of the input file contains integers $n$ and $x_{0}$ ( $1<=n<=100$ ; $0<=x_{0}<=1000$ ). The following $n$ lines contain pairs of integers $a_{i},b_{i}$ ( $0<=a_{i},b_{i}<=1000$ ; $a_{i}≠b_{i}$ ).

Output the required minimum distance in the same units as the positions on the racetrack. If there is no such a position, output -1.