4
1 4
3 1
3 4
 5
4 1
4 3
5 3
2 4
 21
7 15
13 1
14 3
4 10
2 3
16 18
17 20
16 20
8 4
3 12
2 17
13 11
16 1
13 2
13 5
8 9
6 14
3 17
16 9
13 8
 3
3 1
3 2
 6
5 2
5 3
1 4
3 1
5 6
 60
17 34
46 22
50 44
46 33
41 21
31 33
48 6
38 19
35 60
2 24
49 29
7 53
34 1
19 55
32 1
31 42
27 28
4 53
6 50
21 34
1 10
12 36
54 8
16 13
51 43
45 51
54 20
13 53
34 33
49 33
51 11
59 34
15 5
59 28
30 39
13 30
58 4
34 14
3 9
19 34
4 18
26 48
56 54
3 43
57 25
3 41
35 3
48 44
19 13
54 1
23 31
59 47
5 1
46 40
6 26
20 25
37 5
17 24
20 52
 3
3 2
1 2
 39
6 13
15 39
10 35
31 28
4 21
12 39
3 7
3 13
6 1
5 14
36 28
12 15
18 38
30 29
19 34
36 16
20 22
8 13
38 32
26 39
21 37
1 7
15 27
12 26
8 3
6 14
29 2
25 23
32 21
5 16
32 25
6 8
13 10
23 30
34 37
29 33
28 14
36 5
 10
5 9
8 5
7 6
7 9
3 9
2 1
7 2
3 6
7 1

1
3 4 1 2  0
 3
13 2 1 7 3 17 1 19 13 8 1 21  0
 0
 2
48 44 1 6 6 26 1 12  0
 7
12 15 1 2 1 7 1 9 12 26 1 11 8 3 1 12 6 8 1 17 28 14 1 20 36 5 1 24  2
3 6 1 4 7 1 1 10 
import java.util.Iterator;
import java.util.Queue;
import java.util.Scanner;
import java.util.Vector;
import java.util.concurrent.ArrayBlockingQueue;


public class _25D {
	
	static Scanner scanner = new Scanner(System.in);
	static int N, ncom;
	static Vector<Integer>[] vects;
	static int[] com, visit;
	static int[][] mat;
	static Queue<Integer> qu = new ArrayBlockingQueue<Integer>(2000);

	public static void main(String[] args) {
		N = scanner.nextInt();
		vects = new Vector[N+1];
		mat = new int[N+1][N+1];
		for (int i=1;i<=N;++i) {
			vects[i] = new Vector<Integer>();
		}
		for (int i=1;i<=N-1;++i) {
			int fr, to;
			fr = scanner.nextInt();
			to = scanner.nextInt();
			vects[fr].add(to);
			vects[to].add(fr);
			mat[fr][to] = mat[fr][to] = 1;
		}
		com = new int[2000];
		visit = new int[N+1];
		ncom = 0;
		for (int i=1;i<=N;++i) {
			if (visit[i] == 0) {
				ncom++;
				visit[i] = ncom;
				com[ncom] = i;
				dfs(i);
			}
		}

		if (ncom == 1) {
			System.out.println(0);
		}
		else {
			for (int i=2;i<=ncom;++i) {
				System.out.println(qu.poll() + " " + qu.poll() + " " + com[1] + " " + com[ncom]);
			}
		}
	}

	private static void dfs(int i) {
		Iterator<Integer> it = vects[i].iterator();
		while (it.hasNext()) {
			int next = it.next();
			if (visit[next] == 0) {
				visit[next] = ncom;
				dfs(next);
			}
			else {
				if (mat[i][next] == 1) {
					qu.add(i);
					qu.add(next);
					mat[i][next] = mat[next][i] = 0;
				}
			}
		}
		
	}

}
