// Party Invitations — Iterative Elimination O(N²)
#include <iostream>
#include <vector>
using namespace std;

int main() {
    int n;
    cin >> n;
    vector<pair<int,int>> wish(n + 1);
    for (int i = 1; i <= n; i++)
        cin >> wish[i].first >> wish[i].second;

    vector<bool> invited(n + 1, true);
    bool changed = true;

    while (changed) {
        changed = false;
        // Count supporters for each person
        vector<int> support(n + 1, 0);
        for (int i = 1; i <= n; i++) {
            if (!invited[i]) continue;
            support[wish[i].first]++;
            support[wish[i].second]++;
        }
        // Remove anyone with < 2 supporters
        for (int i = 1; i <= n; i++) {
            if (invited[i] && support[i] < 2) {
                invited[i] = false;
                changed = true;
            }
        }
    }

    vector<int> result;
    for (int i = 1; i <= n; i++)
        if (invited[i]) result.push_back(i);

    cout << result.size() << endl;
    for (int i = 0; i < (int)result.size(); i++)
        cout << result[i] << (i+1 < (int)result.size() ? " " : "\n");
    return 0;
}