// Source: https://usaco.guide/general/io

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

int main() {
	int n;
	cin >> n;
	vector<int> db(n + 1);
	vector<pair<int, int>> to(n + 1);
	for (int i = 1; i <= n; i++) {
		int a, b;
		cin >> a >> b;
		db[a]++;
		db[b]++;
		to[i].first = a;
		to[i].second = b;
	}

	queue<int> out;
	for (int i = 1; i <= n; i++) {
		if (db[i] < 2) {
			out.push(i);
			db[i] = -1;
		}
	}

	while (out.size() > 0) {
		//cout << out.front() << "\n";
		db[to[out.front()].first]--;
		db[to[out.front()].second]--;
		if (db[to[out.front()].first] < 2 && db[to[out.front()].first] > -1) {
			out.push(to[out.front()].first);
			db[to[out.front()].first] = -1;
		}
		if (db[to[out.front()].second] < 2 && db[to[out.front()].second] > -1) {
			out.push(to[out.front()].second);
			db[to[out.front()].second] = -1;
		}
		out.pop();
	}

	string ans;
	int cnt = 0;
	for (int i = 1; i <= n; i++) {
		if (db[i] >= 2) {
			ans += to_string(i) + " ";
			cnt++;
		}
	}

	cout << cnt << "\n" << ans;
}