#include <bits/stdc++.h>
using namespace std;
int main() {
    int n; cin >> n;
    vector<int> bf(n+1);
    vector<vector<int>> g(n+1);
    for (int i = 1; i <= n; i++) {
        int a,b; cin >> a >> b;
        bf[a]++;
        bf[b]++;
        g[i].push_back(a);
        g[i].push_back(b);
    }
    bool b = true;
    while (b) {
        b = false;
        for (int i = 1; i <= n; i++) {
            if (g[i].size() > 0 && bf[i] < 2) {
                b = true;
                for (int x : g[i]) bf[x]--;
                g[i].clear();
            }
        }
    }
    vector<int> out;
    for (int i = 1; i <= n; i++) {
        if (bf[i] >= 2) out.push_back(i);
    }
    cout << out.size() << '\n';
    for (int x : out) cout << x << ' ';
}