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 math
from sys import stdin,stdout
from bisect import bisect_left, bisect_right
from copy import deepcopy

def isprime(n):  
    if(n<=1): 
       return False
    if(n<=3) : 
       return True
    if(n%2==0 or n%3==0) : 
       return False
    i=5
    while(i*i<=n) : 
        if(n%i==0 or n%(i+2)==0) : 
           return False
        i=i+6
    return True
def freq(l): #return freq disctionary   
    f = {} 
    for i in l: 
        if (i in f): 
            f[i] += 1
        else:
          f[i] = 1
    return f

MAX = pow(10, 5)
inp=lambda : int(stdin.readline())
sip=lambda : stdin.readline()
mulip =lambda : map(int, stdin.readline().split())
lst=lambda : list(map(int,stdin.readline().split()))
slst=lambda: list(sip())
#-------------------------------------------------------

def find_set(v):
    if d[v]==v:
        return v
    if v in d:
        d[v]=find_set(d[v])
        return d[v]
    
def union(a, b):
    a = d[a]
    b = d[b]
    d[b]=a

def make_set(a, b):
    if a in d and b not in d:
        d[b]=find_set(d[a])
    elif b in d and a not in d:
        d[a] =find_set(d[b])
    elif a in d and b in d:
        if find_set(d[a])==find_set(d[b]):
            arr.append([a,b])
        else:
            d[a] = find_set(d[b])
    else:
        d[b]=a 
        d[a]=a 

N = inp()
d = {}
arr = []
for _ in range(N-1):
    a, b = mulip()
    make_set(a, b)
#print(d)
l = list(d.values())
l = list(set(l))
print(len(l)-1)
for i in range(1,len(l)):
    #print()
    print(*arr[i-1],l[i-1],l[i])
    