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;
const int maxn = 1e3 + 20;
struct point {
  int next;
  int to;
};
struct stt {
  int first;
  int second;
};
stt sto[maxn];
point pt[maxn];
int head[maxn], q, vis[maxn], in[maxn], out[maxn], flag, k, ans;
void add(int u, int v) {
  pt[q].next = head[u];
  pt[q].to = v;
  head[u] = q++;
}
void dfs(int st) {
  vis[st] = 1;
  if (in[st] < 2) ans++;
  for (int i = head[st]; i != -1; i = pt[i].next) {
    int v = pt[i].to;
    if (!vis[v]) {
      if (in[st] >= 2 && out[st] >= 2 && in[v] >= 2 && out[v] >= 2 && !flag) {
        sto[k].first = st;
        sto[k++].second = v;
        flag = 1;
      }
      dfs(v);
    }
  }
}
int main() {
  int n, u, v, po;
  std::ios::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  while (cin >> n) {
    q = 1;
    memset(head, -1, sizeof(head));
    memset(vis, 0, sizeof(vis));
    memset(in, 0, sizeof(in));
    memset(out, 0, sizeof(out));
    k = 0;
    for (int i = 1; i <= n - 1; i++) {
      cin >> u >> v;
      add(u, v);
      add(v, u);
      in[u] += 1;
      out[u] += 1;
      in[v] += 1;
      out[v] += 1;
    }
    for (int i = 1; i <= n; i++) {
      flag = 0;
      ans = 0;
      if (!vis[i]) {
        dfs(i);
        if (ans >= 2 || (in[i] == 0 && out[i] == 0)) po = i;
        if (ans >= 2 && flag) k -= 1;
      }
    }
    cout << k << endl;
    for (int i = 0; i < k; i++) {
      if (!i)
        cout << sto[i].first << " " << sto[i].second << " " << sto[i].second
             << " " << po << endl;
      else
        cout << sto[i].first << " " << sto[i].second << " " << sto[i].second
             << " " << sto[i - 1].first << endl;
    }
  }
  return 0;
}
