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 Solution {

    StreamTokenizer in;
    PrintWriter out;

    public static void main(String[] args) throws Exception {
        new Solution().run();
    }

    int nextInt() throws Exception {
        in.nextToken();
        return (int) in.nval;
    }

    public void run() throws Exception {
        in = new StreamTokenizer(new BufferedReader(new InputStreamReader(System.in)));
        out = new PrintWriter(new OutputStreamWriter(System.out));
        solve();
        out.flush();
    }

    public void solve() throws Exception {
        int n = nextInt();
        long [][] a = new long [2][1200];
        long [] res = new long [1200];
        for (int i=0; i<n;i++)
            res[i]=i+1;
        int q=0;
        for (int i=0;i<n-1;i++)
        {
          int r=nextInt();
          int l=nextInt();
          if (res[r]==res[l])
          {
              a[0][q]=r;
              a[1][q]=l;
              q++;
          } else
          {
              for (int j=0; j<n; j++)
                  if ((j!=l)&&(res[j]==res[l])) res[j]=res[l];
              res[l]=res[r];
          }
        }
        out.println(q);
        for (int w=0; w<q; w++)
        {
            int k=1;
            for (int i=1;i<n;i++)
                if (res[i]!=res[1]) k=i-1;
            out.println(a[0][w]+" "+a[1][w]+" 1 "+k);
            for (int i=1;i<n;i++)
                if ((res[i]==res[k])&&(i!=k)) res[i]=res[0];
            res[k]=res[0];

        }
    }

}
