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 
//25D
//Roads not only in Berland

import java.util.*;

public class BerlandRoads
{
    static int sets;
    static boolean[] isParent;
    static int[] parent, rank;
    static ArrayList<Integer> parents;
    static ArrayList<Integer>[] adjList;

    public static void initializeSets(int size)
    {
        sets = size;
        parent = new int[size + 1];
        rank   = new int[size + 1];
        isParent = new boolean[size + 1];
        Arrays.fill(isParent, true);

        for(int i = 0; i < size + 1; i++) 
            parent[i] = i;
    }

    public static int findSet(int i)
    {
        if(parent[i] == i) return i;
        return findSet(parent[i]);
    }

    public static boolean isSameSet(int i, int j)
    {
        return findSet(i) == findSet(j);
    }

    public static void union(int i, int j)
    {
        int ii = findSet(i);
        int jj = findSet(j);
        if(ii == jj) return;

        sets--;
        if(rank[ii] > rank[jj])
        {
            parent[jj] = ii;
            isParent[jj] = false;
        }
        else
        {
            parent[ii] = jj;
            isParent[ii] = false;            
            if(rank[ii] == rank[jj]) rank[jj]++;
        }
    }

    public static void addParents()
    {
        parents = new ArrayList<>();
        for(int i = 1; i < isParent.length; i++)
            if(isParent[i])
                parents.add(i);
    }

    public static void main(String[] args) 
    {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        initializeSets(n);
        adjList = new ArrayList[n + 1];
        
        for(int i = 0; i < n + 1; i++)
            adjList[i] = new ArrayList<>();

        for(int i = 0; i < n - 1; i++)
        {
            int x = sc.nextInt();
            int y = sc.nextInt();
            union(x, y);
            adjList[x].add(y);
            adjList[y].add(x);
        }

        System.out.println(sets - 1);
        addParents();

        while(parents.size() > 1)
        {
            int x = parents.get(0);
            int y = parents.get(1);
            union(x, y);
            adjList[x].add(y);
            adjList[y].add(x);
            System.out.println(x + " " + adjList[x].get(0) + " " + x + " " + y);
            parents.remove(0);
        }
    }
}