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 
# import sys
# sys.stderr=open('err.txt','w')
# sys.stdout=open('output.txt','w')
# sys.stdin=open('input.txt','r')

def make_set(v):
    parent[v]=v
    rank[v]=1

def find_set(a):
    if parent[a]==a:
        return a
    parent[a]=find_set(parent[a])
    return parent[a]

def union_set(a,b):
    x=find_set(a)
    y=find_set(b)
    if x==y:
        return
    if rank[x]>rank[y]:
        parent[y]=x
        rank[x]+=rank[y]
    else:
        parent[x]=y
        rank[y]+=rank[x]

n=int(input())
a=[_ for _ in range(1,n+1)]
parent=[0]*n
rank=[0]*n

for i in a:
    make_set(i-1)
t=[]
for i in range(n-1):
    p,q=map(int,input().split(' '))

    if find_set(p-1)==find_set(q-1):
        t.append((p-1,q-1))
    else:
        union_set(p-1,q-1)
#print(parent)
#print(rank)
#print(t)
u=[]
for i in parent:
    if i not in u:
        u.append(i)
x=len(t)
if len(u)<=1:
    print("0")
else:
    for i in range(1,len(u)):
        if x>0:
            print(str(t[0][0]+1)+" "+str(t[0][1]+1)+" "+str(t[0][1]+1)+" "+str(u[i]+1))
