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.*;
import java.io.*;
public class DisjointSet {
	
	private static int[] ind;
	private static int[] sz;
	
	
	public static void main(String[] args) throws NumberFormatException, IOException {
		BufferedReader rd = new BufferedReader(new InputStreamReader(System.in));
		int n = Integer.parseInt(rd.readLine());
		
		sz = new int[n];
		ind = new int[n];
		for (int i = 0; i < n; i++) {
			ind[i] = i;
			sz[i] = 1;
		}
		
		
		ArrayList<String> starr = new ArrayList<String>();
		StringTokenizer tk = null;
		
		for (int i = 0; i < n - 1; i++) {
			tk = new StringTokenizer(rd.readLine());
			int a = Integer.parseInt(tk.nextToken()) - 1;
			int b = Integer.parseInt(tk.nextToken()) - 1;
			boolean isCon = isConnect(a, b);
			if(isCon) starr.add((a + 1) + " " + (b + 1));
			else connect(a, b);
			
		}
		
		ArrayList<Integer> arr = new ArrayList<>();
		for (int i = 0; i < n; i++) {
			if(!arr.contains(root(i))) arr.add(root(i));
		}
		System.out.println(Arrays.toString(ind));
		System.out.println(arr);

		System.out.println(starr.size());
		if(starr.size() == 0) return;
		for (int i = 1; i < arr.size(); i++) {
			System.out.println(starr.get(i - 1) + " " + (arr.get(i) + 1) + " " + (arr.get(i - 1) + 1));
		}
		
	}
	
	private static int root(int i){
		while(i != ind[i]){
			ind[i] = ind[ind[i]];
			i = ind[i];
			
		}
		
		return i;
	}
	
	private static boolean isConnect(int a, int b){
		
		if(root(a) == root(b)) return true;
		
		return false;
	}
	
	
	private static void connect(int a, int b){
		int a1 = root(a);
		int b1 = root(b);
		if(sz[a1] >= sz[b1]){
			ind[b1] = a1;
			sz[a1] += sz[b1];
		}
		else {
			ind[a1] = b1;
			sz[b1] += a1;
		}
		
	}
	
}
