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 
n=int(input())
a=[[] for i in range(n)]
for i in range(n):
    for j in range(n):
        if i!=j:
            a[i].append([j+1,1])
        else:
            a[i].append([j+1,1000000000000000000])
d=[]
e=[]
for i in range(n-1):
    u,v=list(map(int,input().split()))
    a[u-1][v-1][1]=0
    a[v-1][u-1][1]=0
    e.append(sorted([u,v])+[1])
b=[[-1,-1] for i in range(n)]
c=[0]*n
c[0]=2
t=0
for i in a[0]:
    if i[0]!=1:
        b[i[0]-1]=[i[1],1]
        c[i[0]-1]=1
for i in range(n-1):
    z=-1
    for j in range(n):
        if c[j]==1 and (z==-1 or b[j][0]<b[z][0]):
            z=j
    c[z]=2
    t+=b[z][0]
    e.append(sorted([b[z][1],z+1])+[2])
    for j in a[z]:
        if j!=z+1:
            if c[j[0]-1]==0:
                c[j[0]-1]=1
                b[j[0]-1]=[j[1],z+1]
            else:
                if j[1]<b[j[0]-1][0]:
                    b[j[0]-1]=[j[1],z+1]
e.sort()
f=[]
g=[]
for i in range(len(e)):
    if e[i][2]==2:
        if not(i and e[i-1][0]==e[i][0] and e[i-1][1]==e[i][1]):
            g.append([e[i][0],e[i][1]])
    else:
        if not(2*n-3-i and e[i+1][0]==e[i][0] and e[i+1][1]==e[i][1]):
            f.append([e[i][0],e[i][1]])
print(t)
for i in range(t):
    print(*f[i]+g[i])