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 <iostream>
#include <iomanip>
#include <fstream>
#include <sstream>
#include <cmath>
#include <cstdio>
#include <string>
#include <vector>
#include <algorithm>
#include <cstdlib>
#include <cstring>
#include <map>
#include <queue>
#include <set>
#include <queue>
#include <stack>
#include <deque>
#include <assert.h>
#include <ctime>
#include <bitset>
#include <numeric>
#include <complex>
#include <conio.h>
using namespace std;

#define FOR(i, a, n) for (register int i = (a); i < (int)(n); ++i)
#define Size(n) ((int)(n).size())
#define ll long long
#define pb push_back
#define X first
#define Y second
#define EPS 1e-10
#define mp make_pair
#define MFOR(i,m,n) for(int i=m;i>n;i--)
#define error(x) cerr<<endl<<x<<endl;
#define st return 0;

void error2(const string &s,const int &t){
    cerr<<endl<<"  "<<s<<" = "<<t<<endl;
}

const int N=1000+2;
pair <int,int> e;
int mrk[N],ee[N][N][2],sum,end=0;
vector <int> adj[N],be[N];
vector <pair <int,int> > ce,com;

void DFS(int v){
    FOR(i,0,adj[v].size()){
        if(mrk[adj[v][i]]){
            ee[v][adj[v][i]][0]++;
            ee[adj[v][i]][v][0]++;
            if(ee[adj[v][i]][v][0] == 2){
                ce.pb(mp(v,adj[v][i]));
                ee[v][adj[v][i]][1]=com[Size(com)-1].X;
                ee[adj[v][i]][v][1]=com[Size(com)-1].X;
            }
        }
        if(!mrk[adj[v][i]]){
            be[end].pb(adj[v][i]);
            mrk[adj[v][i]]++;
            sum++;
            DFS(adj[v][i]);
        }
    }
}

int main(){
    int n,begin=-1;
    cin>>n;
    FOR(i,0,n-1){
        cin>>e.X>>e.Y;
        e.X--;
        e.Y--;
        adj[e.X].pb(e.Y);
        adj[e.Y].pb(e.X);
    }
    while(sum<n){
        FOR(i,0,n)
            if(!mrk[i]++){
                sum++;
                begin=i;
                break;
            }
        be[end].pb(begin);
        int temp=Size(com);
        com.pb(mp(begin,temp));
        DFS(begin);
        end++;
    }
    FOR(i,0,end)
        sort(be[i].begin(),be[i].end());
    cout<<Size(com)-1<<endl;
    FOR(i,0,Size(com)-1){
        int temp=com[Size(com)-i-1].Y;
        if(binary_search(be[temp].begin(),be[temp].end(),ee[ce[i].X][ce[i].Y][1])){
            swap(com[Size(com)-i-1],com[0]);
        }
        cout<<ce[i].X+1<<" "<<ce[i].Y+1<<" "<<ce[i].X+1<<" "<<com[Size(com)-i-1].X+1<<endl;
    }
    st;
}
