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

int main() {
	int n; cin >> n;
    vector<int>ind(n);
    vector<vector<int>>g(n);
    vector<bool>participants(n, 1);
    for(int i  = 0; i < n; i++)
    {
        int a, b; cin >> a >> b;
        a--, b--;
        g[i].push_back(a);
        g[i].push_back(b);
        ind[a]++;
        ind[b]++;
    }
    bool removing = 1;
    int ans = n;
    while(removing)
    {
        removing = 0;
        for(int i = 0; i < n; i++)
        {
            if(ind[i] < 2 && participants[i])
            {
                removing = 1;
                participants[i] = 0;
                for(int p : g[i])ind[p]--;
                ans--;
            }
        }
    }
    cout << ans << "\n";
    for(int i = 0; i < n; i++)
    {
        if(participants[i])cout << i + 1 << " ";
    }
    cout << "\n";
}