ENET

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

const int N = 2005;

int n, m, s, t;
vector<int> a[N];
int ans;
int isCut[N], child[N], ok[N], vs[N];
int step;
int low[N], num[N], d[N], e[N];

void visit(int u) {
    low[u] = num[u] = ++step;

    for(int v : a[u]) {
        if(v == d[u]) continue;

        if(num[v])
            low[u] = min(low[u], num[v]);
        else {
            d[v] = u;
            visit(v);
            low[u] = min(low[u], low[v]);
        }
    }
}

void bfs(int u, int pa, int d[]) {
    queue<int> q;
    fill(d + 1, d + n + 1, 0);
    d[u] = d[pa] = 1;
    q.push(u);

    if(u == pa) return;

    while(!q.empty()) {
        u = q.front();
        q.pop();

        for(int v : a[u]) {
            if(d[v]) continue;
            d[v] = 1;
            q.push(v);
        }
    }
}

int connected(int u, int v) {
    vs[u] = 1;
    if(u == v) return 1;

    for(int uv : a[u])
        if(!vs[uv] && connected(uv, v))
            return 1;

    return 0;
}

int main() {
    //freopen("in.txt", "r", stdin);
    freopen("ENET.inp", "r", stdin);
    freopen("ENET.out", "w", stdout);
    ios_base::sync_with_stdio(false);
    cin.tie(NULL); cout.tie(NULL);

    cin >> n >> m >> s >> t;
    for(int i = 1; i <= m; i++) {
        int x, y; cin >> x >> y;
        a[x].push_back(y);
        a[y].push_back(x);
    }

    if(!connected(s, t)) {
        cout << 0 << '\n';
        return 0;
    }

    for(int i = 1; i <= n; i++)
        if(!d[i]) visit(i);

    for(int i = 1; i <= n; i++)
        child[d[i]]++;

    for(int i = 1; i <= n; i++)
        if(d[i] && !isCut[d[i]])
            if(low[i] >= num[d[i]] && (d[d[i]] || child[d[i]] > 1))
                isCut[d[i]] = 1;
    fill(ok + 1, ok + n + 1, 1);

    for(int i = 1; i <= n; i++)
        if(isCut[i]) {
            bfs(s, i, d);
            bfs(t, i, e);

            for(int j = 1; j <= n; j++)
                ok[j] &= (d[j] | e[j]);
        }

    for(int i = 1; i <= n; i++)
        ans += ok[i];

    cout << ans << '\n';

    vector<int> res;
    for(int i = 1; i <= n; i++)
        if(ok[i])  cout << i << '\n';

    return 0;
}