#include <bits/stdc++.h>

using namespace std;

int main() {
    iostream::sync_with_stdio(0);
    cin.tie(0);
    int N;
    cin >> N;
    vector<int> edgesA(N), edgesB(N);
    vector<int> invitee_counter(N, 0);
    for(int i = 0, a, b; i < N; ++i) {
        cin >> edgesA[i] >> edgesB[i];
        --edgesA[i];
        --edgesB[i];
        ++invitee_counter[edgesA[i]];
        ++invitee_counter[edgesB[i]];
    }
    list<int> nodes;
    for(int i = 0; i < N; ++i) nodes.push_back(i);
    bool changes = true;
    while(nodes.size() > 0 && changes) {
        auto it = nodes.begin();
        changes = false;
        while(it != nodes.end()) {
            if(invitee_counter[*it] >= 2) {
                ++it;
                continue;
            }
            changes = true;
            --invitee_counter[edgesA[*it]];
            --invitee_counter[edgesB[*it]];
            auto del_it = it;
            ++it;
            nodes.erase(del_it);
        }
    }
    vector<int> nodes_out;
    nodes_out.reserve(nodes.size());
    for(int x : nodes) nodes_out.push_back(x);
    sort(nodes_out.begin(), nodes_out.end());
    cout << nodes_out.size() << "\n";
    for(auto n : nodes_out) cout << n + 1 << " ";
    cout << "\n";
    return 0;
}