Given a connected graph with n nodes and m edges, where m <= n.You are also given two nodes a and b of the graph.
You need to find the number of edges which are present in all paths between a and b.
CONSTRAINTS:
1 <= N <= 105
N-1 <= M <= min(105,N)
1 <= a,b <= N possibly a = b.
INPUT FORMAT :
The First line contains two space separated integers N and M, the number of nodes and edges respectively.
The second line contains two space separated integers a and b.
Then m lines follow, the i-th line contains two integers xi and yi (1≤xi,yi≤n, xi≠yi) --- the endpoints of the i-th edge.
OUTPUT FORMAT :
The output should contain a single number which is the number of edges present in all paths between a and b.
The edge (3,5) lies in all paths between node 2 and 5. This is the only edge which occurs in every path between 2 and 5.
Therefore, the answer is 1.
