#include <bits/stdc++.h>
using namespace std;
int n;
vector<int> adj[1000005];
vector<int> leaves;
int main() {
ios_base::sync_with_stdio(false);
cin.tie(nullptr);
cin >> n;
for (int i = 1; i < n; i++) {
int u, v;
cin >> u >> v;
adj[u].push_back(v);
adj[v].push_back(u);
}
for (int i = 1; i <= n; i++) {
if (adj[i].size() == 1) {
leaves.push_back(i);
}
}
int k = (leaves.size() + 1) / 2;
cout << k << '\n';
for (int i = 0; i < leaves.size() / 2; i++) {
cout << leaves[i] << " " << leaves[i + (leaves.size() + 1) / 2] << '\n';
}
if (leaves.size() % 2 == 1) {
cout << leaves[(leaves.size() - 1) / 2] << " " << leaves.back() << '\n';
}
return 0;
}
