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;
#define rep(i,a,n) for(__typeof(n)i=a;i<n;i++)
#define pb push_back
#define pp pop_back
#define pf push_front
#define ppf pop_front
#pragma GCC target ("avx2")
#pragma GCC optimization ("O3")
#pragma GCC optimization ("unroll-loops")
#define uu first
#define vv second
#define mxel max_element
#define minel min_element
#define mpit map<int,int>::iterator it
#define mpits map<string,int>::iterator it
#define sit set<int>s::iterator it
#define be(x) x.begin(),x.end()
#define lbs(x,num) lower_bound(x.begin(),x.end(),num)
#define ubs(x,num) upper_bound(x.begin(),x.end(),num)
#define vit vector<int>::iterator it
#define ll long long int
#define ull unsigned long long int
#define end1 "\n"
#define ld long double
#define inout freopen("in.txt","r",stdin);freopen("out.txt","w",stdout);
#define cas int t;cin>>t;while(t--)
#define cases int t;cin>>t;for(int i=1;i<=t;i++)
#define faster ios::sync_with_stdio(false);cin.tie(NULL);cout.tie(NULL);
#define mem(x,val) memset(x,val,sizeof(x))
#define sett(val) fixed<<setprecision(val)
#define pii pair<int,int>
#define pi acos(-1)
#define nu 10000000007
#define mod (int)1e9+7
#define valid(x,y,row,column) x>0&&x<=row&&y>0&&y<=column


ll lcm(ll a,ll b)
{
    return (a*b)/__gcd(a,b);
}
struct node{
int x,y;
};
bool cmp(int a,int b)
{
    return a>b;
}
bool cmp1(pii a,pii b)
{
    return a.uu<b.uu;
}
ll bigmod(ll a,ll b,ll m)
{
    if(b==0) return 1;
    ll x=bigmod(a,b/2,m);
    x=(x*x)%m;
    if(b%2) x=(x*a)%m;
    return x;
    //if(ans<0) ans+=m;
}
//macro defined
//if my code doesn't work,i'll kill everyone CZ i'm not Robert Bruce
//Coding korle ki fash taka pabo?
//thak fash taka lagbe na emni i coding korbo
//Chadni raate bodna hate
//when you need more precision than float::prepare for trouble,make it double!!
//stack-overflow:do you trust me?::with every cell of my body
//let's start the code
int dirx[]={0,0,+1,-1};
int diry[]={+1,-1,0,0};
int p[1009];
int findx(int x)
{
    if(p[x]==x) return x;
    return p[x]=findx(p[x]);
}
void uni(int x,int y)
{
    int a=findx(x);
    int b=findx(y);
        p[a]=b;
}
void solve()
{
    int n;
    cin>>n;
    vector<pii>v,v1;
    for(int i=1;i<=n;i++) p[i]=i;
    for(int i=1;i<n;i++)
    {
        int x,y;
        cin>>x>>y;
        if(findx(x)==findx(y))
        v.pb({x,y});
        else uni(x,y);
    }
    for(int i=2;i<=n;i++)
    {
        if(findx(1)!=findx(i))
        {
            v1.pb({1,i});
        }
    }
    cout<<v.size()<<endl;
    for(int i=0;i<v.size();i++)
    {
        cout<<v[i].uu<<" "<<v[i].vv<<" "<<v1[i].uu<<" "<<v1[i].vv<<endl;
    }
}
//i am a noob ,so please don't hack my code
//check corner test cases:)

int main(){
    faster
    //cas
 // cases
solve();

}
//The code ends here.RTE and WA is my regular partner
//to avoid RTE check array size and array bounds:v
