Fragile network

import sys 

input = sys.stdin.read().split()

n = int(input[0])
t = [[] for _ in range(n+1)]

i = 1
for _ in range(n-1):
    a = int(input[i])
    b = int(input[i+1])
    t[a].append(b)
    t[b].append(a)
    i +=2

leaf = []
for i in range(1,n+1) : 
    if len(t[i]) == 1 : 
        leaf.append(i)

k = len(leaf)
ans = (k+1)//2
print(ans)
half = k//2
for i in range(ans):
    p1 = leaf[i]
    p2 = leaf[(i + half) % k]
    print(p1, end = " ")
    print(p2)   

Test 1

Verdict: ACCEPTED

Test 2

Verdict: ACCEPTED

Test 3

Verdict: ACCEPTED

Test 4

Verdict: ACCEPTED

Test 5

Verdict: ACCEPTED

Test 6

Verdict: ACCEPTED

Test 7

Verdict: ACCEPTED

Test 8

Verdict: WRONG ANSWER

Test 9

Verdict: ACCEPTED

Test 10

Verdict: ACCEPTED

Test 11

Verdict: ACCEPTED

Test 12

Verdict: ACCEPTED

Test 13

Verdict: ACCEPTED

Test 14

Verdict: ACCEPTED

Test 15

Verdict: ACCEPTED

Test 16

Verdict: ACCEPTED

Test 17

Verdict: ACCEPTED

Test 18

Verdict: ACCEPTED

Test 19

Verdict: WRONG ANSWER

Test 20

Verdict: ACCEPTED

Test 21

Verdict: WRONG ANSWER