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

#define int long long
#define pb push_back
#define mp make_pair
#define fi first
#define se second

struct edge {
    int from, to, weight;
    edge() : from(0), to(0), weight(0) {}
    edge(int from_, int to_, int weight_) : from(from_), to(to_), weight(weight_) {}
};

const int maxn = 1e5;
const int inf = 1e16;

int n, m, start, last;
vector<edge> graph[maxn + 1];
vector<edge> edges;
int dist[maxn + 1];
bool done[maxn + 1];

void dijkstra() {
    for(int i = 1; i <= n; i++) {
        dist[i] = inf;
    }
    priority_queue<pair<int, int> > q;
    q.push(mp(0, last));
    dist[last] = 0;
    while(!q.empty()) {
        pair<int, int> p = q.top();
        q.pop();
        int cur_dist = -p.fi, cur = p.se;
        if(done[p.se]) {
            continue;
        }
        done[cur] = true;
        for(edge nei : graph[cur]) {
            if(cur_dist + nei.weight < dist[nei.to]) {
                dist[nei.to] = cur_dist + nei.weight;
                q.push(mp(-(cur_dist + nei.weight), nei.to));
            }
        }
    }
}

int comp_cnt;
int comp[maxn + 1];
vector<int> by_comp[maxn + 1];
vector<int> graph_comps[maxn + 1];
int dp[maxn + 1];
int pre[maxn + 1];

void dfs(int cur) {
    comp[cur] = comp_cnt;
    by_comp[comp_cnt].pb(cur);
    for(edge nei : graph[cur]) {
        if((dist[nei.to] == dist[cur]) && !comp[nei.to]) {
            dfs(nei.to);
        }
    }
}

bool better(int a, int b) {
    return dist[by_comp[a][0]] < dist[by_comp[b][0]];
}

void solve() {
    cin >> n >> m >> start >> last;
    for(int i = 1; i <= m; i++) {
        int a, b, c;
        cin >> a >> b >> c;
        edges.pb(edge(a, b, c));
        graph[a].pb(edge(a, b, c));
        graph[b].pb(edge(b, a, c));
    }
    dijkstra();
    for(int i = 1; i <= n; i++) {
        if(!comp[i]) {
            comp_cnt++;
            dfs(i);
        }
    }
    for(edge e : edges) {
        if(dist[e.from] < dist[e.to]) {
            graph_comps[comp[e.to]].pb(comp[e.from]);
        }
        if(dist[e.from] > dist[e.to]) {
            graph_comps[comp[e.from]].pb(comp[e.to]);
        }
    }
    vector<int> comps(comp_cnt, 0);
    for(int i = 0; i < comp_cnt; i++) {
        comps[i] = i + 1;
    }
    sort(comps.begin(), comps.end(), better);
    for(int cur : comps) {
        for(int nei : graph_comps[cur]) {
            if(dp[cur] < dp[nei]) {
                dp[cur] = dp[nei];
                pre[cur] = nei;
            }
        }
        dp[cur] += (int) by_comp[cur].size();
    }
    cout << dp[comp[start]] << "\n";
    /*for(int i = 1; i <= n; i++) {
        cout << dist[i] << " ";
    }
    cout << "\n";
    for(int i = 1; i <= comp_cnt; i++) {
        cout << dp[i] << " " << pre[i] << " - ";
        for(int x : by_comp[i]) {
            cout << x << " ";
        }
        cout << "\n";
    }*/
    vector<int> ans_comps;
    int tmp = comp[start];
    ans_comps.pb(tmp);
    while(tmp != comp[last]) {
        tmp = pre[tmp];
        ans_comps.pb(tmp);
    }
    vector<int> ans;
    for(int x : ans_comps) {
        for(int y : by_comp[x]) {
            ans.pb(y);
        }
    }
    sort(ans.begin(), ans.end());
    for(int x : ans) {
        cout << x << " ";
    }
    cout << "\n";
}

signed main() {
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    solve();
    return 0;
}