// Baltic Olympiad in Informatics 2015 Day 1 Problem 3
// Network
// https://oj.uz/problem/view/BOI15_net
#include <bits/stdc++.h>
using namespace std;
int N;
vector<int> adjList[500001];
vector<int> leaf;
void DFS(int node, int parent) {
int numOfVertices = 0;
for (auto child: adjList[node]) {
numOfVertices++;
if (child != parent) {
DFS(child, node);
}
}
if (numOfVertices == 1) {
leaf.push_back(node);
}
}
int main() {
cin >> N;
for (int i = 1; i < N; i++) {
int u, v;
cin >> u >> v;
adjList[u].push_back(v);
adjList[v].push_back(u);
}
DFS(1, -1);
int k = (int)leaf.size();
if (k % 2 == 0) {
cout << k/2 << "\n";
for (int i = 0; i < k/2; i++) {
cout << leaf[i] << " " << leaf[i+k/2] << "\n";
}
}
else {
cout << k/2+1 << "\n";
for (int i = 0; i < k/2; i++) {
cout << leaf[i] << " " << leaf[i+k/2] << "\n";
}
cout << leaf[k/2] << " " << 1 << "\n";
}
}
