SP185 CHASE1 - Chase

Chase is a two-person board game. A board consists of squares numbered from 1 to _n_. For each pair of different squares it is known if they are adjacent to one another or they are not. Each player has a piece at his disposal. At the beginning of a game pieces of players are placed on fixed, distinct squares. In one turn a player can leave his piece on the square it stands or move it to an adjacent square. A game board has the following properties: - it contains no triangles, i.e. there are no three distinct squares such that each pair of them is adjacent, - each square can be reached by each player.

The number of test cases _t_ is in the first line of input, then _t_ test cases follow separated by an empty line. In the first line of a test case there are four integers _n_, _m_, _a_ and _b_ separated by single spaces, where 2

For each test case you should output one line containing: - one word "No", if player B cannot catch player A, or - one integer - the number of turns needed by B to catch A (if B can catch A).