#include <bits/stdc++.h>
using namespace std;
using ll = long long;
const int MOD = 1e9 + 7;
const int N = 1e5 + 11;
int n;
vector<int> adj[N], leaf;
void sol() {
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) {
leaf.push_back(i);
}
}
int sz = leaf.size();
cout << (sz + 1) / 2 << '\n';
for (int i = 0; i + 1 < sz; i += 2) {
cout << leaf[i] << ' ' << leaf[i + 1] << '\n';
}
if (sz % 2 == 1) {
cout << leaf[sz - 1] << ' ' << 1 << '\n';
}
}
int main() {
ios_base::sync_with_stdio(false);
cin.tie(nullptr);
int t = 1;
//cin >> t;
while (t--) {
sol();
}
}
