#include <bits/stdc++.h>
using namespace std;
using ll = long long;
const ll maxN = 2e5 + 5;


vector<vector<pair<ll, ll> > > g;
vector<ll> dist;
vector<ll> p(maxN), s(maxN, 1);
vector<set<ll> > to(maxN);
vector<bool> volt(maxN, 0);

ll root(ll x) {
    if(p[x] == x) return x;

    return p[x] = root(p[x]);
}

void connect(ll x, ll y) {
    x = root(x);
    y = root(y);

    if(x == y) return;
    if(s[x] < s[y]) swap(x, y);

    p[y] = x;
    s[x] += s[y];
}

void dijkstra(ll start) {
    priority_queue<pair<ll, ll> > pq;
    pq.push({0, start});

    while (!pq.empty()) {
        auto curr = pq.top();
        pq.pop();

        ll w = -curr.first, x = curr.second;
        if(dist[x] != -1) continue;
        dist[x] = w;
        for(pair<ll, ll> sz : g[x]) {
            if(dist[sz.first] != -1) continue;
            pq.push({-w-sz.second, sz.first});
        }
    }
}

void dfs(int x) {
    volt[x] = 1;
    for(int sz : to[x]) {
        if(volt[sz]) continue;
        dfs(sz);
    }
}

int main() {

    ios::sync_with_stdio(0);cin.tie(0); cout.tie(0);
    
    ll n,m,a,b;
    cin >> n >> m >> a >> b;
    g.resize(n+1);
    dist.resize(n+1, -1);

    for(ll i = 0; i < m; i++) {
        ll x,y,z;
        cin >> x >> y >> z;

        g[x].push_back({y, z});
        g[y].push_back({x, z});
    }

    dijkstra(b);
    for(int i = 1; i <= n; i++) p[i] = i;
    for(ll i = 1; i <= n; i++) {
        for(auto sz : g[i]) {
            if(dist[sz.first] == dist[i]) {
                connect(sz.first, i);
            }
        }
    }
    for(ll i = 1; i <= n; i++) {
        for(auto sz : g[i]) {
            if(dist[sz.first] < dist[i]) {
                to[root(i)].insert(root(sz.first));
            }
            else if(dist[sz.first] > dist[i]) {
                to[root(sz.first)].insert(root(i));
            }
        }
    }

    dfs(root(a));
    vector<ll> be(n+1, 0);
    for(ll i = 1; i <= n; i++) {

        if(!volt[i] || root(i) != i) continue;
        for(ll sz : to[i]) be[root(sz)]++;
    }

    vector<ll> tav(n+1, -1), parent(n+1, -1);
    
    tav[root(a)] = 0;
    queue<ll> sor;
    sor.push(root(a));
    while(!sor.empty()) {
        ll cur = sor.front();
        sor.pop();

        for(ll sz : to[cur]) {
            be[sz]--;
            if(tav[sz] < tav[cur] + s[cur]) {
                tav[sz] = tav[cur] + s[cur];
                parent[sz] = cur;
            }
            if(be[sz] == 0) {
                sor.push(sz);
            }
        }
    }

    set<ll> mo = {root(b)};
    ll cur = root(b);
    while(cur != root(a)) {
        cur = parent[cur];
        mo.insert(cur);
    }
    
    vector<ll> ki;
    for(ll i = 1; i <= n; i++) {
        if(mo.find(root(i)) != mo.end()) ki.push_back(i);
    }

    cout << ki.size() << "\n";
    for(ll sz : ki) cout << sz << ' ';
    
    return 0;
}