#include <bits/stdc++.h>
using namespace std;
 
const int MAXN = 105;
vector<int> adj[MAXN];
bool visited[MAXN];
int n, m, u, v;
int criticalCount = 0; // Bi?n d?m s? d?nh th?t
 
void dfs(int node, int blocked) {
    if (node == blocked) return; // Không xét d?nh b? ch?n
    visited[node] = true;
    for (int neighbor : adj[node]) {
        if (!visited[neighbor]) {
            dfs(neighbor, blocked);
        }
    }
}
 
bool isCritical(int s) {
    fill(visited, visited + n + 1, false);
    dfs(u, s); // Th? b? d?nh s và ki?m tra du?ng di t? u d?n v
    return !visited[v]; // N?u không d?n du?c v, thì s là d?nh th?t
}
 
int main() {
    cin >> n >> m >> u >> v;
    for (int i = 0; i < m; i++) {
        int a, b;
        cin >> a >> b;
        adj[a].push_back(b);
        adj[b].push_back(a);
    }
 
    vector<int> criticalNodes;
    for (int s = 1; s <= n; s++) {
        if (s != u && s != v && isCritical(s)) {
            criticalNodes.push_back(s);
            criticalCount++; // Tang bi?n d?m
        }
    }
 
    cout << criticalCount << endl;
    for (int s : criticalNodes) {
        cout << s << " ";
    }
    if (criticalCount > 0) cout << endl;
 
    return 0;
}
 

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