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.math.BigInteger;
import java.util.*;

public class SolveContest {
    PrintWriter out;
    BufferedReader input;
    long begin;

    SolveContest(String infile, String outfile) {
        try {
            input = new BufferedReader(new FileReader(infile));
            out = new PrintWriter(new FileWriter(outfile), true);
            solver();
        } catch (Exception ex) {
            ex.printStackTrace();
            input = new BufferedReader(new InputStreamReader(System.in));
            out = new PrintWriter(System.out, true);
            solver();
        } finally {
            out.close();
            try {
                input.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }

    void startTime() {begin = System.currentTimeMillis();}
    long getTime() {return System.currentTimeMillis()-begin;}

    StringTokenizer st = new StringTokenizer("");

    private String nextToken() {
        while (!st.hasMoreElements()) {
            try {
                st = new StringTokenizer(input.readLine());
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        return st.nextToken();
    }

    private int nextInt() {
        return Integer.parseInt(nextToken());
    }

    private long nextLong() {
        return Long.parseLong(nextToken());
    }

    private double nextDouble() {
        return Double.parseDouble(nextToken());
    }
    int[] p;
    int dsu_get(int x) {
        return (x == p[x]) ? x : (p[x] = dsu_get(p[x]));
    }

    void solver() {
        int n = nextInt();
        p = new int[n];
        for (int i = 0; i < n; i++)
            p[i] = i;
        List<Integer>[] lists = new List[n];
        for (int i = 0; i < n-1; i++) {
            int a = nextInt()-1;
            int b = nextInt()-1;
            int a1 = dsu_get(a);
            int b1 = dsu_get(b);
            if (a1 == b1) {
                if (lists[a] == null)
                    lists[a] = new LinkedList<>();
                lists[a].add(b);
            } else {
                p[a1] = b1;
            }
        }
        int from = dsu_get(0);
        Set<Integer> set = new HashSet<>();
        set.add(from);
        StringBuilder sb = new StringBuilder();
        String[] ans = new String[1005];
        int c = 0;
        for (int i = 1; i < n; i++) {
            int k = dsu_get(i);
            if (from != k && !set.contains(k)) {
                set.add(k);
                for (int j = 0; j < n; j++) {
                    if (lists[j] != null && lists[j].size() > 0) {
                        sb.append(j+1).append(" ")
                                .append(lists[j].get(lists[j].size()-1)+1).append(" ")
                                .append(1).append(" ")
                                .append(i+1);
                        ans[c++] = sb.toString();
                        sb = new StringBuilder();
                        p[j] = p[lists[j].get(lists[j].size()-1)];
                        lists[j].remove(lists[j].size()-1);
                        break;
                    }
                }
            }
        }
        out.println(c);
        for (int i = 0; i < c; i++) {
            out.println(ans[i]);
        }
    }

    public static void main(String[] args) {
        new SolveContest("input.txt","output.txt");
    }
}