？！？

#include<iostream>
#include<cstring>
#include<set>
using namespace std;
int map[51][51];
int deg[51];
bool vis[51]; 
set<int> colorList;
int ans[1001];
int order = 0;
void dfs1(int node) {
	vis[node] = true;
	for (int color:colorList) if (map[node][color] && !vis[color]) {
		dfs1(color);
	}
}
void dfs2(int node) {
	//不必回溯状态，如果路没走完，for循环会继续，达成插入的效果
	for (int color : colorList) if (map[node][color]) {
		map[node][color]--;
		map[color][node]--;
		dfs2(color);
	}
	ans[order++] = node; //已经走过的必然是最后的顺序
}
int main(){
	int t,n,from ,to;
	cin >> t;
	for (int a = 1; a <= t; a++) { 
		memset(map, 0, sizeof map);
		memset(deg, 0, sizeof deg);
		memset(vis, 0, sizeof vis);
		order = 0;
		colorList.clear();
		cin >> n; 
		for (int i = 0; i < n; i++) {
			cin >> from >> to;
			map[from][to]++;
			map[to][from]++;
			deg[from]++;
			deg[to]++;
			colorList.insert(from);
			colorList.insert(to); 
		}
		cout << "Case #" << a << endl;
		bool able = true;
		dfs1(*colorList.begin());
		for (int color: colorList) {
			if (!vis[color]) {
				able = false;
				break;
			}
			if (deg[color] % 2) {
				able = false;
				break;
			}
		}
		if (able == false) {
			cout << "some beads may be lost" << endl;
		}
		else {
			dfs2(*colorList.begin());
			for (int i = n-1; i >=0; i--) cout << ans[i+1] << " " << ans[i] << endl;
		}
		
		cout << endl;
	}
	return 0;
}