#include <algorithm>
#include <bits/stdc++.h>

using namespace std;
using ll = long long;

const int MAXN = 100'001;

vector<pair<int, ll>> g[MAXN];
vector<int> g2[MAXN];
int dp[MAXN], comp[MAXN], nxt[MAXN], n, m, a, b;
ll dist[MAXN];

void dijkstra(int source) {
	fill(dist, dist+MAXN, 1e18);
	priority_queue<pair<ll, int>, vector<pair<ll, int>>, greater<pair<ll, int>>> pq;
	dist[source] = 0;
	pq.push({0, source});
	while (!pq.empty()) {
		auto [d, u] = pq.top(); pq.pop();
		if (dist[u] != d) continue;
		for (auto [v, w] : g[u]) {
			if (dist[v] > dist[u] + w) {
				dist[v] = dist[u] + w;
				pq.push({dist[v], v});
			}
		}
	}
}

void dfs(int u, int c) {
	comp[u] = c;
	for (auto [v, w] : g[u]) {
		if (!comp[v] && dist[u] == dist[v]) dfs(v, c);
	}
}

int timer = 1;
void build_graph() {
	for (int i = 1; i <= n; i++) {
		if (!comp[i]) dfs(i, timer++);
	}
	for (int i = 1; i <= n; i++) {
		for (auto [u, w] : g[i]) {
			if (dist[i] > dist[u]) g2[comp[i]].emplace_back(comp[u]);
		}
	}
	for (int i = 1; i < timer; i++) {
		sort(g2[i].begin(), g2[i].end());
		g2[i].erase(unique(g2[i].begin(), g2[i].end()), g2[i].end());
	}
}

int longest_route(int u) {
	if (dp[u] == -1) {
		dp[u] = INT_MIN;
		for (int v : g2[u]) {
			if (dp[u] < longest_route(v) + 1) {
				nxt[u] = v;
				dp[u] = dp[v] + 1;
			}
		}
	}
	return dp[u];
}

int main() {
	ios::sync_with_stdio(0); cin.tie(0);
	fill(dp, dp+MAXN, -1);
	cin >> n >> m >> a >> b;
	for (int i = 0; i < m; i++) {
		int u, v; ll w; cin >> u >> v >> w;
		g[u].emplace_back(v, w);
		g[v].emplace_back(u, w);
	}
	dijkstra(b);
	build_graph();
	dp[comp[b]] = 0;
	int u = comp[a];
	vector<int> good = {comp[b]};
	while (u != comp[b]) {
		good.emplace_back(u);
		u = nxt[u];
	}
	sort(good.begin(), good.end());
	vector<int> ans;
	for (int i = 1; i <= n; i++) {
		if (binary_search(good.begin(), good.end(), comp[i])) ans.emplace_back(i);
	}
	cout << ans.size() << "\n";
	for (int u : ans) cout << u << " ";
	cout << "\n";
	return 0;
}