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.Scanner;
import java.util.Stack;

/**
 ** Created by Alik on 10/25/2015.
 */
public class Problem_25D {
  


    public static boolean[][] destroy;
    public static boolean[] disconnected;
    public static boolean[] visited;
    public static boolean[][] edges;
    public static Stack<Integer> stack = new Stack<Integer>();
    public static int count = 0;
    public static int city;

    public static void main(String[] args){
        Scanner in = new Scanner(System.in);
        city = in.nextInt();

        disconnected = new boolean[city];
        destroy = new boolean[city][city];
        edges = new boolean[city][city];
        int a, b;
        int start = 0;
        for (int i = 0; i < city-1; i++){
            a = in.nextInt();
            start = a;
            b = in.nextInt();
            edges[a-1][b-1] = true;
            edges[b-1][a-1] = true;
        }

        visited = new boolean[city];

        for (int i = 0; i < city; i++){
            if (!visited[i]) {
                if (i != 0) {
                    disconnected[i] = true;
                    disconnected[i-1] = true;
                }
                DFS(i);
            }
        }
        int first = -1;
        String[] disArray = new String[city];
        int index = 0;
        for (int i = 0; i < disconnected.length; i++) {
            if (disconnected[i] && first <= 0){
                first = i;
            }
            else if (disconnected[i] && first > 0){
                disArray[index] = (first+1) + " " + (i+1);
                first = -1;
                index++;
            }
        }
        if (first > 0){
            disArray[index] = (first+1) + " " + (start+1);
        }
        index = 0;
        System.out.println(count);
        for (int i = 0; i < destroy.length; i++) {
            for (int j = 0; j < destroy.length; j++) {
                if (destroy[i][j]){
                    System.out.print((i+1) + " " +(j+1) + " ");
                    System.out.print((disArray[index]));
                    System.out.println();
                    index++;
                }
            }
        }

    }
    public static void DFS(int i){
        visited[i] = true;
        for(int j = 0; j < edges.length; j++){
            if (edges[i][j] && !visited[j]) {
                edges[i][j] = false;
                edges[j][i] = false;
                DFS(j);
            }
            else if( edges[i][j] && visited[j]){
                destroy[i][j] = true;
                //disconnected[i] = true;
                edges[i][j] = false;
                edges[j][i] = false;
                count++;
            }
        }
        stack.push(i);
    }
}
