#include <bits/stdc++.h>
using namespace std;
bool visited[500000];
#pragma GCC optimize("O3,unroll-loops")
#pragma GCC target("avx2,bmi,bmi2,lzcnt,popcnt")
int main() {
ios_base::sync_with_stdio(false);
cin.tie(NULL);
int n, d1,d2; cin >> n;
vector<vector<int>> graph(n);
for (int i=0;i<n-1;i++) {
cin >> d1 >> d2; d1--; d2--;
graph[d1].push_back(d2);
graph[d2].push_back(d1);
visited[i] = false;
}
visited[n - 1] = false;
vector<int> leaves;
stack<int> dfs; dfs.push(0);
int node;
bool flag;
if (graph[0].size() == 1) {leaves.push_back(0);}
while (dfs.size() > 0) {
flag = false;
node = dfs.top(); dfs.pop();
visited[node] = true;
for (int i: graph[node]) {
if (!visited[i]) {
dfs.push(i);
flag = true;
}
}
if (!flag) {
leaves.push_back(node);
}
}
int m = leaves.size();
cout << (m + 1) / 2 << '\n';
for (int i=0;i<m/2;i++) {
cout << leaves[i] + 1 << ' ' << leaves[i + (m / 2)] + 1 << '\n';
}
if (m % 2 == 1) {
cout << leaves[m - 1] + 1 << ' ' << leaves[m - 1 - (m / 2)] + 1 ;
}
}
