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;
long long int nodes_size;
long long int edge_size;
class edge {
 public:
  long long int node;
  long long int cost;
  edge(long long int i, long long int j) {
    node = i;
    cost = j;
  }
};
class graph {
 public:
  long long int node;
  vector<edge> edges;
  long long int parent;
  long long int cost;
  vector<long long int> children;
} nodes[1005];
long long int visited[1005];
class point {
 public:
  long long int x;
  long long int y;
  point() {}
  point(long long int i, long long int j) {
    x = i;
    y = j;
  }
};
void fill_array(long long int ar[], long long int value, long long int size) {
  for (long long int i = 0; i < size; i++) ar[i] = value;
}
void print_ll_vector(vector<long long int> v) {
  for (long long int i = 0; i < v.size(); i++) cout << v[i] << " ";
  cout << endl;
}
void input_graph(bool is_undirected, bool is_cost) {
  cin >> nodes_size;
  edge_size = nodes_size - 1;
  for (long long int i = 0; i < edge_size; i++) {
    long long int a, b, c;
    cin >> a >> b;
    if (is_cost) {
      cin >> c;
      nodes[a].edges.push_back(edge(b, c));
      if (is_undirected) nodes[b].edges.push_back(edge(a, c));
    } else {
      nodes[a].edges.push_back(edge(b, 1));
      if (is_undirected) nodes[b].edges.push_back(edge(a, 1));
    }
  }
}
long long int ctr = 0;
vector<pair<long long int, pair<long long int, long long int> > >
    destroyed_edges;
vector<pair<long long int, long long int> > new_edges;
void dfs(long long int node, long long int parent) {
  visited[node] = 1;
  for (long long int i = 0; i < nodes[node].edges.size(); i++) {
    if (nodes[node].edges[i].node != parent) {
      if (visited[nodes[node].edges[i].node]) {
        if (node < nodes[node].edges[i].node) {
          destroyed_edges.push_back(
              make_pair(ctr, make_pair(node, nodes[node].edges[i].node)));
        }
      } else {
        dfs(nodes[node].edges[i].node, node);
      }
    }
  }
}
long long int check[1005];
int main() {
  input_graph(true, false);
  fill_array(visited, 0, nodes_size + 1);
  for (long long int i = 1; i <= nodes_size; i++) {
    if (!visited[i]) {
      ctr++;
      if (i != 1) {
        new_edges.push_back(make_pair(i, ctr));
      }
      dfs(i, -1);
    }
    if (i == 1 && destroyed_edges.size() != 1)
      new_edges.push_back(make_pair(1, ctr));
  }
  fill_array(check, 0, new_edges.size());
  cout << new_edges.size() << endl;
  for (long long int i = 0; i < new_edges.size(); i++) {
    for (long long int j = 0; j < destroyed_edges.size(); j++) {
      if (!check[j] && new_edges[i].second != destroyed_edges[j].first) {
        cout << destroyed_edges[j].second.first << " "
             << destroyed_edges[j].second.second << " "
             << destroyed_edges[j].second.first << " " << new_edges[i].first
             << endl;
        check[j] = 1;
        break;
      }
    }
  }
  return 0;
}
