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

#define all(v) v.begin(),v.end()
using ll = long long;
using ull = unsigned long long;
using vll=vector<ll>;
using vvll = vector<vector<ll>>;
const ll INF=1ll<<60;
using vp=vector<pair<ll, ll>>;
using P = pair<ll,ll>;


struct unionfind{
    ll N;
    vector<ll> par,Rank,Size;
    unionfind(ll n):N(n){
        par=vector<ll>(N),Rank=vector<ll>(N,1),Size=vector<ll>(N,1);
        for(int i=0;i<N;i++) par[i]=i;
    };
    ll find(ll x){
        if(par[x]==x) return x;
        else return par[x]=find(par[x]);
    }

    bool same(ll a,ll b){
        return find(a)==find(b);
    }

    void unite(ll a,ll b){
        if(same(a,b))return;
        a=find(a);
        b=find(b);
        ll s=Size[a]+Size[b];
        if(Rank[b]>Rank[a]) par[a]=b;
        else par[b]=a;
        if(Rank[a]==Rank[b]) Rank[a]++;
        Size[find(a)]=s;
    }

    ll size(ll a){
       return Size[find(a)];
    }
};

int main(){
    ll N;
    cin>>N;
    unionfind uf(2e5);
    vll A(2e5);
    vvll ab(2e5);
    vp hw(N);
    vll deg(2e5);
    set<P> st;
    for(int i=0;i<N;i++){
        cin>>hw[i].first>>hw[i].second;
        hw[i].first--;hw[i].second--;
        if(hw[i].first!=hw[i].second){
            A[hw[i].second]++;
            deg[hw[i].first]++;
            deg[hw[i].second]++;
        ab[hw[i].first].push_back(hw[i].second);
        }else st.insert(make_pair(hw[i].first,hw[i].second));
        uf.unite(hw[i].first,hw[i].second);
    }
    ll s=uf.find(hw[0].first);
    for(int i=0;i<N;i++){
        if(uf.find(hw[i].first)!=s){
            cout << 0 << endl;
            return 0;
        }
    }
    queue<ll> q;
    for(int i=0;i<2e5;i++){
        if(A[i]==0&&ab[i].size())q.push(i);
    }
    ll cnt=0;
    bool a=true;
    while(!q.empty()){
        auto x=q.front();q.pop();
        if(q.size()!=0)a=false;
        cnt++;
        for(auto to:ab[x]){
            A[to]--;
            if(A[to]==0)q.push(to);
        }
    }
    if(cnt==N){
        if(a)cout << 1 << endl;
        else cout << 0 <<endl;
        return 0;
    }
    for(int i=0;i<2e5;i++){
        if(ab[i].size()){
            if(deg[i]!=2){
                cout<<0<<endl;
                return 0;
            }
        }
    }
    vll n;
    ll now=hw[0].first;
    for(int i=0;i<N+1;i++){
        n.push_back(now);
        now=ab[now][0];
    }
    for(int i=0;i<N;i++){
        st.insert(make_pair(n[i+1],n[i]));
      cout<<n[i]<<endl;
    }
    cout <<st.size()<< endl;
        
}