#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <vector>
#include <cmath>
#include <cstring>
#include <string>
#include <iterator>
#include <iomanip>
#include <queue>
#include <stack>
using namespace std;

#define sqr(x) ((x)*(x))
#define cbr(x) ((x)*(x)*(x))
#define rep(c, i, n) for((i)=(c); (i)<(n); (i)++)
/**
//Geometry

struct pt { long long x, y; };
double vecmul(pt a, pt b) { return (a.x*b.y - b.x*a.y); }

double dist(double ax, double ay, double bx, double by) { return sqrt(sqr(ax - bx) + sqr(ay - by)); }
*/

//DBG
template<typename T, typename T2>void printarr(T  a[], T2 sz, T2 beg = 0) { for (T2 i = beg; i<sz; i++) cout << a[i] << " "; cout << endl; }
#define DBG(a)         cout<<#a<<"="<<(a)<<"\n"
#define DBG2(a,b)       cout<<#a<<"="<<(a)<<", "<<#b<<"="<<(b)<<"\n"
#define DBG3(a,b,c)     cout<<#a<<"="<<(a)<<", "<<#b<<"="<<(b)<<", "<<#c<<"="<<(c)<<"\n"

//Files
#define FILE_MODE(FILE) freopen(FILE".in", "r", stdin), freopen(FILE".out", "w", stdout)

//Constants
#define PI    3.1415926535897932
#define INF   1011111111
#define LLINF 1000111000111000111LL
#define eps   1e-14
#define mod   1000000007
#define ll long long
#define ull unsigned long long
//-------------------------------------------------
#define N 50010
//7 9 1 7 3 6 1 3 6 7 1 4 5 6  1 2 2 5 3 5  4 7 
int n, m, s, f;
vector<int> vertex[N];
queue<int> bfsQ;
vector<int> path[N];
int vis[N];
int dist[N];

int main() {
	cin >> n >> m >> s >> f;
	s--; f--;
	int i,x,y,j;
	rep(0,i,m) {
		cin >> x >> y;
		x--; y--;
		vertex[x].push_back(y);
		vertex[y].push_back(x);
	}
	//visited 0, distance to everything is inf.
	memset(dist, -1, sizeof dist);
	memset(vis, 0, sizeof vis);

	dist[s] = 0;
	vis[s] = 1;
	path[s].push_back(s);

	bfsQ.push(s);
	int minDist=-1;
	while (!bfsQ.empty()) {
		int u = bfsQ.front();

		bfsQ.pop();

		for (int i : vertex[u]) {
			if (!vis[i]) {
				vis[i] = 1;
				dist[i] = dist[u]+1;
				path[i] = path[u];
				path[i].push_back(i);
				bfsQ.push(i);
			}
		}
	}
	cout << dist[f] << endl;
	rep(0, i, path[f].size()) {
		path[f][i]++;
	}
	copy(path[f].begin(), path[f].end(), ostream_iterator<int>(cout, " "));
	return 0;
}