#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<tuple<int,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,i);
		g[b].emplace_back(a,w,i);
	}
	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>ans,a;
	int ansc=0,ac=0;
	vector<int>v(N+1),w(M);
	int st=clock();
	auto bt=[&](auto self,int i)->void{
		if(clock()-st>CLOCKS_PER_SEC)return;
		if(v[i]==0){
			ac++;
		}
		v[i]++;
		a.push_back(i);
		if(i==B){
			if(ac>ansc){
				ansc=ac;
				ans=a;
			}
		}
		else{
			for(auto[j,_,k]:g[i]){
				if(w[k]>=2){
					continue;
				}
				w[k]++;
				if(c[j]<=c[i]){
					self(self,j);
				}
				w[k]--;
			}
		}
		a.pop_back();
		v[i]--;
		if(v[i]==0){
			ac--;
		}
	};
	bt(bt,A);
	sort(ans.begin(),ans.end());
	ans.erase(unique(ans.begin(),ans.end()),ans.end());
	cout<<ans.size()<<'\n';
	for(int i:ans){
		cout<<i<<' ';
	}
	cout<<'\n';
	return 0;
}