Two Fairs

Description:

Input:

The first line of the input contains an integer $$$t$$$ ($$$1 \le t \le 4\cdot10^4$$$) — the number of test cases in the input. Next, $$$t$$$ test cases are specified.

The first line of each test case contains four integers $$$n$$$, $$$m$$$, $$$a$$$ and $$$b$$$ ($$$4 \le n \le 2\cdot10^5$$$, $$$n - 1 \le m \le 5\cdot10^5$$$, $$$1 \le a,b \le n$$$, $$$a \ne b$$$) — numbers of cities and roads in Berland and numbers of two cities where fairs are held, respectively.

The following $$$m$$$ lines contain descriptions of roads between cities. Each of road description contains a pair of integers $$$u_i, v_i$$$ ($$$1 \le u_i, v_i \le n$$$, $$$u_i \ne v_i$$$) — numbers of cities connected by the road.

Each road is bi-directional and connects two different cities. It is guaranteed that from any city you can pass to any other by roads. There can be more than one road between a pair of cities.

The sum of the values of $$$n$$$ for all sets of input data in the test does not exceed $$$2\cdot10^5$$$. The sum of the values of $$$m$$$ for all sets of input data in the test does not exceed $$$5\cdot10^5$$$.

Output:

Print $$$t$$$ integers — the answers to the given test cases in the order they are written in the input.

Sample Input:

3
7 7 3 5
1 2
2 3
3 4
4 5
5 6
6 7
7 5
4 5 2 3
1 2
2 3
3 4
4 1
4 2
4 3 2 1
1 2
2 3
4 1

Sample Output:

4
0
1