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.io.*;
import java.util.*;

public class Div25 {
    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        InputReader in = new InputReader(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
		TaskD taskd = new TaskD();
		taskd.solve(in, out);
        out.close();
    }
	static class TaskD {
		private int n;
		private int[] parent;
		private ArrayList<Pair<Integer, Integer>> close = new ArrayList<>();
		private ArrayList<Pair<Integer, Integer>> build = new ArrayList<>();
		private void makeSet(int v) {
			parent[v] = v;
		}
		private int findSet(int v) {
			if(v == parent[v]) {
				return v;
			}
			return parent[v] = findSet(parent[v]);
		}
		private void merge(int a, int b) {
			int x = findSet(a);
			int y = findSet(b);
			if(x == y) {
				close.add(new Pair<>(a, b));
			} else {
				parent[x] = y;
			}
		}
		public void solve(InputReader in, PrintWriter out) {
			n = in.nextInt();
			parent = new int[n+1];
			for(int i = 1; i <= n; i++)makeSet(i);
			int x, y;
			for(int i = 0; i < n-1; i++) {
				x = in.nextInt();
				y = in.nextInt();
				merge(x, y);
			}
			for(int i = 2; i <= n; i++) {
				x = findSet(1);
				y = findSet(i);
				if(x != y) {
					merge(x, y);
					build.add(new Pair<Integer, Integer>(1, i));
				}
			}
			if(build.size() == 0) {
				out.println("0");
				return;
			}
			for(int i = 0; i < build.size(); i++) {
				out.println(close.get(i).left + " " + close.get(i).right + " " + build.get(i).left + " " + build.get(i).right);
			}
		}
	}
    static class InputReader {
        public BufferedReader reader;
        public StringTokenizer tokenizer;

        public InputReader(InputStream stream) {
            reader = new BufferedReader(new InputStreamReader(stream));
            tokenizer = null;
        }

        public String next() {
            while (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
            return tokenizer.nextToken();
        }

        public int nextInt() {
            return Integer.parseInt(next());
        }
        public long nextLong() {
            return Long.parseLong(next());
        }

        public double nextDouble() {
            return Double.parseDouble(next());
        }

    }
	static class Pair<L,R> {
		public L left;
		public R right;
		public Pair(L a, R b) {
			left = a;
			right = b;
		}
		public Pair(){}
	}
}