#include <iostream>
#include <vector>

using namespace std;


int main(){
    int n,m,a,b;

    cin>>n>>m>>a>>b;
    a--;
    b--;
    vector<vector<int> > gr(n);
    int x,y;
    for(int i = 0; i<m; i++){
        cin>>x>>y;
        x--;
        y--;
        gr[x].push_back(y);
        gr[y].push_back(x);
    }

    vector<int> level(n, 0);

    vector<bool> visited(n, false);

    vector<long long> count_(n, 0);

    vector<int> q;

    q.push_back(a);

    visited[a] = true;
    count_[a] = 1;
    int j = 1;

    while(! q.empty()){
        vector<int> next;
        for(int o = 0; o<q.size();o++){
            int node = q[o];
            int child;
            for(int i = 0; i<gr[node].size(); i++){
                child = gr[node][i];
                if( visited[child] == false){
                    level[child] = j;
                    count_[child] = count_[node];
                    next.push_back(child);
                    visited[child] = true;
                }
                else if(level[child] == j){
                    count_[child] += count_[node];
                }

            }
        }
        q = next;
        j++;
    }
    cout<<count_[b]%(1000000007);


}