#include <iostream>
#include <cstdio>
#include <vector>
#include <queue>
#include <cstring>
#include <map>

using namespace std;

#define DIM 8000

int N, M, x, y;

vector <vector <int> > G;
vector <vector <int> > D;
queue <pair <int, int> > Q;
int was[DIM];
map <int, vector <int> > myMap;
vector <int> ans;

void BF(int, int, int);

int main() {
    freopen("graf.in","r",stdin);
    freopen("graf.out","w",stdout);

    scanf("%d %d %d %d\n", &N, &M, &x, &y);

    G.resize(N + 1);
    D.resize(2, vector <int> (N + 1));

    int a, b;
    for(int i = 1; i <= M; ++i) {
        scanf("%d %d\n", &a, &b);

        G[a].push_back(b);
        G[b].push_back(a);
    }

    Q.push(make_pair(x, 0));
    was[x] = 1;
    BF(x, 0, 0);
    memset(was, 0, sizeof(was));
    was[y] = 1;
    Q.push(make_pair(y, 0));
    BF(y, 0, 1);

    int mn = 2e9;

    for(int i = 1; i <= N; ++i) {
        if(mn > D[0][i] + D[1][i]) {
            mn = D[0][i] + D[1][i];
        }
    }

    for(int i = 1; i <= N; ++i) {
        if(mn == D[0][i] + D[1][i]) {
            myMap[D[0][i]].push_back(i);
        }
    }

    for(int i = 1; i <= N; ++i) {
        if(mn == D[0][i] + D[1][i]) {
            if(myMap[D[0][i]].size() == 1) {
                ans.push_back(myMap[D[0][i]][0]);
            }
        }
    }

    cout << ans.size() << '\n';

    for(unsigned int z = 0;z < ans.size(); ++z) {
        cout << ans[z] << ' ';
    }

    cout << '\n';

    return 0;
}

void BF(int node, int dist, int root) {
    if(Q.empty()) {
        return ;
    }

    Q.pop();

    D[root][node] = dist;

    for(unsigned int z = 0; z < G[node].size(); ++z) {
        if(!was[G[node][z]]) {
            Q.push(make_pair(G[node][z], dist + 1));
            was[G[node][z]] = 1;
        }
    }

    node = Q.front().first;
    dist = Q.front().second;

    BF(node, dist, root);
}