#include "bits/stdc++.h"
using namespace std;
#define ff first
#define ss second
#define int long long
#define pii pair<int,int>
#define pb emplace_back
#define rep(i,a,b) for(int i=a; i < b; ++i)
#define owo ios::sync_with_stdio(0); cin.tie(0); cout.tie(0);
#define V vector

#define cerr if(1) cout
#define dbg(x) cerr << "?" << #x << " : " << x << endl;

void solve();
signed main(){
	owo
	int t = 1; //cin >> t
	while(t--) solve();
}

const int N = 1e5+5;


int n;
array<int,2> edg[N];
V<int> adj[N];

int r[4];

int d[N], p[N];
void dfs(int x,int par){
	for(int e : adj[x]){
		int y = edg[e][0]^edg[e][1]^x;
		if(y==par) continue;
		bool isr = 0;
		rep(i,0,4){
			isr |= y==r[i];
		}
		if(isr) continue;

		p[y] = p[x];
		d[y] = d[x]+1;
		dfs(y, x);
	}
}


bool g[4][4], gvis[4];
int gdfs(int x){
	if(gvis[x]) return 0;
	gvis[x] = 1;

	int ret = 1;
	rep(y,0,4) if(g[x][y]){
		ret += gdfs(y);
	}
	return ret;
}


void solve(){
	cin >> n;

	rep(e,1,n){
		int u, v;
		cin >> u >> v;

		edg[e] = {u,v};
		adj[u].push_back(e);
		adj[v].push_back(e);
	}

	r[1] = -1;
	rep(e,1,n){
		auto[u,v] = edg[e];
		if(adj[u].size()>=2 && adj[v].size()>=2){
			r[1] = u; r[2] = v; break;
		}
	}
	if(r[1]==-1){
		cout << -1 << '\n'; return;
	}

	for(int e : adj[r[1]]){
		int x = edg[e][0]^edg[e][1]^r[1];
		if(x!=r[2]){
			r[0] = x; break;
		}
	}
	for(int e : adj[r[2]]){
		int x = edg[e][0]^edg[e][1]^r[2];
		if(x!=r[1]){
			r[3] = x; break;
		}
	}

	rep(i,0,4){
		// dbg(r[i]);
		p[r[i]] = i;
		dfs(r[i], r[i]);
	}
	g[0][1] = g[1][2] = g[2][3] = 1;
	g[3][2] = g[2][1] = g[1][0] = 1;


	rep(e,1,n){
		auto[u,v] = edg[e];

		if(d[u]==0 && d[v]==0){
			int i = p[u], j = p[v];
			g[i][j] = g[j][i] = 0;

			bool found = 0;
			rep(ii,0,4) if(!found) rep(jj,0,ii-1) if(!found)
			if(!g[ii][jj]){
				g[ii][jj] = g[jj][ii] = 1;
				gvis[0] = gvis[1] = gvis[2] = gvis[3] = 0;
				if(gdfs(r[0])==4){
					found = 1;
					cout << r[ii] << " " << r[jj] << "\n";
				}
				else{
					g[ii][jj] = g[jj][ii] = 0;
				}
			}

		}
		else{
			if(!(d[u]<d[v])) swap(u,v);

			cout << v << " " << r[(p[v]+1)%4] << "\n";
		}

	}	


}