#include <bits/stdc++.h>
using namespace std;
#define int long long
#define INF 9e18
void solve() {
int n;
cin >> n;
vector<vector<int>> adj(n);
for (int i = 1; i < n; i++) {
int u, v; cin >> u >> v; u--, v--;
adj[u].push_back(v);
adj[v].push_back(u);
}
vector<bool> leaf(n);
for (int u = 0; u < n; u++) {
if (adj[u].size() == 1) {
leaf[u] = true;
}
}
vector<bool> vis(n); // applies only to leaves
function<pair<int, int>(int, int, int)> dfs = [&](int u, int p, int d) {
int max_dist = -INF;
int ans_node = -1;
if (p != -1 && leaf[u] && !vis[u]) {
//printf("found leaf\n");
return make_pair(u, d);
}
for (int v : adj[u]) {
if (v == p) continue;
//printf("%lld\n", v + 1);
auto [leaf, dist] = dfs(v, u, d + 1);
if (dist > max_dist) {
max_dist = dist;
ans_node = leaf;
}
}
return make_pair(ans_node, max_dist);
};
vector<pair<int, int>> ans;
int first_leaf = -1;
for (int u = 0; u < n; u++) {
if (!leaf[u]) continue;
if (first_leaf == -1) first_leaf = u;
if (vis[u]) continue;
vis[u] = true;
int v = dfs(u, -1, 0).first;
if (v != -1) {
vis[v] = true;
} else {
v = first_leaf;
}
ans.push_back({u, v});
}
cout << ans.size() << "\n";
for (auto [u, v] : ans) {
cout << u + 1<< " " << v + 1 << "\n";
}
}
signed main() {
ios_base::sync_with_stdio(0);
cin.tie(0);
solve();
return 0;
}
