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 
#include <bits/stdc++.h>
using namespace std;
class DSU {
  vector<int> size;
  vector<int> parent;

 public:
  DSU(int n) {
    size = vector<int>(n, 1);
    parent = vector<int>(n);
    for (int i = 0; i < n; i++) parent[i] = i;
  }
  int set_find(int node) {
    if (node != parent[node]) {
      return parent[node] = set_find(parent[node]);
    }
    return node;
  }
  bool set_union(int node1, int node2) {
    int parent1 = set_find(node1);
    int parent2 = set_find(node2);
    cout << node1 << ' ' << parent1 << " - " << node2 << ' ' << parent2 << endl;
    if (parent1 != parent2) {
      if (size[parent1] < size[parent2]) swap(parent1, parent2);
      parent[parent2] = parent1;
      size[parent1] += size[parent2];
      return false;
    }
    return true;
  }
};
int main() {
  std::ios::sync_with_stdio(0);
  int n;
  cin >> n;
  DSU dsu = DSU(n + 1);
  vector<string> out;
  while (n-- > 1) {
    int a, b;
    cin >> a >> b;
    if (dsu.set_union(a, b)) {
      int pa = dsu.set_find(pa);
      out.push_back(to_string(a) + ' ' + to_string(b) + ' ' + to_string(a) +
                    ' ' + to_string(pa));
    }
  }
  cout << out.size() << '\n';
  for (int i = 0; i < out.size(); i++) cout << out[i] << '\n';
}
