# 制約確認

from collections import deque, defaultdict as dd
from copy import deepcopy
from heapq import heappop, heappush, heappushpop, heapify
from random import randint, seed, shuffle, choice, choices, sample
from time import time

INF = 1 << 60
MOD = 998244353


class Unionfind:
    def __init__(self, num):
        self.num = num
        self.parents = [-1for _ in range(num)]

    def find(self, x):
        if self.parents[x] < 0:
            return x
        else:
            self.parents[x] = self.find(self.parents[x])
            return self.parents[x]

    def union(self, x, y):
        x = self.find(x)
        y = self.find(y)

        if x == y:
            return
        if self.find(x) > self.find(y):
            x, y = y, x
        self.parents[x] += self.parents[y]
        self.parents[y] = x

    def size(self, x):
        return -self.parents[self.find(x)]

    def same(self, x, y):
        return self.find(x) == self.find(y)


def main():
    n, u, v = map(int, input().split())
    e = [list(map(int, input().split())) for _ in range(n-1)]
    assert 3 <= n <= 100000
    assert 1 <= u < v <= n-1
    uf = Unionfind(n)
    for u, v in e:
        assert 1 <= u < v <= n
        if uf.same(u-1, v-1):
            assert 1 < 0
        uf.union(u-1, v-1)


def no():
    print(n, s, t)
    for i in range(m - 1):
        print(i + 1, i + 2)
    for i in range(m, n):
        print(randint(2, m - 1), i + 1)


def nso():
    with open("output.txt", "w") as f:
        print(n, s, t, file=f)
        for i in range(m - 1):
            print(i + 1, i + 2, file=f)
        for i in range(m, n):
            print(randint(2, m - 1), i + 1, file=f)


if __name__ == "__main__":
    main()