#include<bits/stdc++.h>
#define int long long
#define matsuri pair<int,int>
const int iris = 1e9+7;
//const int iris = 998244353;
using namespace std;

int cc=2;

vector<int> G[100001],path;
int dis[100001], v[100001];
int cnt[100001];

int dfs1(int a,int f,int d)
{
	v[a]=1;
	dis[a]=d;
	path.emplace_back(a);
	for(int b:G[a])
	{
		if(b==f)
			continue;
		if(dis[b])
		{
			int cy=d-dis[b]+1;
			if(!cnt[cy])
				cnt[cy]=1;
			else
			{
				dis[a]=0;
				path.pop_back();
				return cy;
			}
		}
		else
		{
			int cy=dfs1(b,a,d+1);
			if(cy)
			{
				dis[a]=0;
				path.pop_back();
				return cy;
			}
		}
	}
	path.pop_back();
	dis[a]=0;
	return 0;
}

void dfs2(int a,int f,int d,int k)
{
	if(!cc)
		return;
	v[a]=2;
	dis[a]=d;
	path.emplace_back(a);
	for(int b:G[a])
	{
		if(b==f)
			continue;
		if(dis[b])
		{
			int cy=d-dis[b]+1;
			if(cy==k)
			{
				int i=path.size();
				while(1)
				{
					i--;
					cout<<path[i]<<' ';
					if(path[i]==b)
						break;
				}
				cout<<'\n';
				cc--;
			}
		}
		else
			dfs2(b,a,d+1,k);
	}
	path.pop_back();
	dis[a]=0;
	return;
}

signed main()
{
    ios::sync_with_stdio(0);
    cin.tie(0);
	
	int n;
	cin>>n;
	for(int i=0;i<n*2-3;i++)
	{
		int a,b;
		cin>>a>>b;
		G[a].emplace_back(b);
		G[b].emplace_back(a);
	}
	int k=-1;
	for(int i=1;i<=n;i++)
	{
		if(v[i]<1)
		{
			k=dfs1(i,0,1);
			if(k!=-1)
				break;
		}
	}
	cout<<k<<'\n';
	for(int i=1;i<=n;i++)
	{
		if(v[i]<2)
			dfs2(i,0,1,k);
	}

    return 0;
}