#include <bits/stdc++.h>
using namespace std;

#define int long long

#define INF (int)1e18

template<typename T>
using min_priority_queue=priority_queue<T,vector<T>,greater<T>>;

signed main(){
	ios::sync_with_stdio(false);
	cin.tie(nullptr);
	int N,M,A,B;
	cin>>N>>M>>A>>B;
	vector<vector<pair<int,int>>>g(N+1);
	for(int i=0;i<M;i++){
		int a,b,w;
		cin>>a>>b>>w;
		g[a].emplace_back(b,w);
		g[b].emplace_back(a,w);
	}
	vector<int>c(N+1,INF);
	min_priority_queue<pair<int,int>>pq;
	c[B]=0;
	pq.emplace(0,B);
	while(!pq.empty()){
		auto[d,i]=pq.top();
		pq.pop();
		if(d>c[i]){
			continue;
		}
		for(auto[j,w]:g[i]){
			if(c[i]+w<c[j]){
				c[j]=c[i]+w;
				pq.emplace(c[j],j);
			}
		}
	}
	vector<int>v(N+1),a(N+1),b(N+1);
	int ap=0,bp=0;
	int it=0;
	auto bt=[&](auto self,int i)->void{
		if(it++>100000000){
			return;
		}
		if(v[i]){
			return;
		}
		v[i]=1;
		a[ap++]=i;
		if(i==B){
			if(ap>bp){
				bp=ap;
				b=a;
			}
		}
		else{
			for(auto[j,_]:g[i]){
				if(c[j]<=c[i]){
					self(self,j);
				}
			}
		}
		ap--;
		v[i]=0;
	};
	bt(bt,A);
	b.resize(bp);
	sort(b.begin(),b.end());
	cout<<b.size()<<'\n';
	for(int i:b){
		cout<<i<<' ';
	}
	cout<<'\n';
	return 0;
}