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;
vector<int> vr[1001];
bool used[1001];
vector<pair<int, int> > cycles;
vector<bool> check;
vector<int> comp;
int DFS(int cur, int parent) {
  used[cur] = true;
  for (int i = 0; i < vr[cur].size(); i++) {
    if (vr[cur][i] != parent) {
      if (used[vr[cur][i]]) {
        cycles.push_back(make_pair(cur, vr[cur][i]));
        check.push_back(false);
      } else
        DFS(vr[cur][i], cur);
    }
  }
}
int main() {
  int n;
  scanf("%d", &n);
  int a, b;
  for (int i = 0; i < n - 1; i++) {
    scanf("%d %d", &a, &b);
    vr[a].push_back(b);
    vr[b].push_back(a);
  }
  bool found;
  int count = 0;
  while (true) {
    found = false;
    for (int i = 1; i <= n; i++) {
      if (!used[i]) {
        found = true;
        DFS(i, 0);
        comp.push_back(i);
        break;
      }
    }
    if (!found) break;
    count++;
  }
  cout << count - 1 << endl;
  for (int i = 1; i < comp.size(); i++) {
    for (int j = 0; j < check.size(); j++) {
      if (!check[j]) {
        printf("%d %d ", cycles[j].first, cycles[j].second);
        check[j] = true;
        for (int k = j + 1; k < cycles.size(); k++) {
          if (cycles[k].first == cycles[j].second &&
              cycles[j].first == cycles[k].second)
            check[k] = true;
          break;
        }
        break;
      }
    }
    printf("1 %d\n", comp[i]);
  }
}
