// UUID: 2907c23f-c678-4ee8-8e59-670c72cdc5fe
#include <bits/stdc++.h>
using namespace std;
using ll=long long;

#define all(a) a.begin(), a.end()
#define rall(a) a.rbegin(), a.rend()
#define vi vector<int>
#define pii pair<int,int>

const int maxn=1e5+1;

vector<pair<int,ll>> g[maxn];
vector<int> g1[maxn];
ll d[maxn];
int n,m,a,b;
vector<int> val(maxn, -1);
vector<int> reach;

int group[maxn];
vector<vector<int>> groups;
int p[maxn];

void dfs(int v){
    reach.push_back(v);
    val[v]=0;
    for (int to : g1[v]){
        if (d[to]<d[v] && val[to]>val[v]){
            val[v]=val[to];
            p[v]=to;
        }
    }
    for (int to : g1[v]){
        if (d[to]>d[v]) continue;
        if (val[to]!=-1) continue;
        dfs(to);
        if (val[to]>val[v]){
            val[v]=val[to];
            p[v]=p[to];
        }
    }
}

void solve(){
    cin>>n>>m>>a>>b;
    for (int i=0;i<m;i++){
        int u,v,c;
        cin>>u>>v>>c;
        g[u].push_back({v,c});
        g[v].push_back({u,c});
    }
    priority_queue<pair<ll,int>> q;
    q.push({0, b});
    vector<pair<ll,int>> srt = {{0,b}};
    fill(d, d+maxn, -1);
    d[b]=0;

    while (!q.empty()){
        auto [dist, v] = q.top();
        q.pop();
        srt.push_back({d[v], v});
        if (d[v]< -dist) continue;
        for (auto [to,c] : g[v]){
            if (d[to]==-1 || d[v]+c<d[to]){
                d[to]=d[v]+c;
                q.push({-d[to], to});
            }
        }
    }
    sort(all(srt));
    for (int i=1;i<=n;i++){
        for (auto [to, c] : g[i]) if (d[i]>=d[to]) g1[i].push_back(to);
    }
    for (auto [_, v] : srt){
        if (val[v]!=-1) continue;
        reach.clear();
        dfs(v);
        val[v]+=reach.size();
        groups.push_back({});
        for (int i : reach){
            groups.back().push_back(i);
            group[i]=groups.size()-1;
            val[i] = val[v];
            p[i]=p[v];
        }
    }
    cout<<val[a]<<"\n";
    int track=a;
    while(track!=b){
        for (int i : groups[group[track]]) cout<<i<<" ";
        track=p[track];
    }
    cout<<b;
}

int main() {
    ios_base::sync_with_stdio(0);cin.tie(0);
    int t=1;
    //cin>>t;
    while (t--){
        solve();
    }
}