#include <bits/stdc++.h>
using namespace std;
vector<vector<int>> adj;
vector<pair<int, int>> ans;
vector<bool> is_leaf;
pair<int, int> dfs(int u, int p = -1, int d = 0) {
if (is_leaf[u] && p != -1) {
return {d, u};
}
int bestd = -1, besti = -1;
for (int v : adj[u])
if (v != p) {
auto [subd, subi] = dfs(v, u, d + 1);
if (subd > bestd) {
bestd = subd;
besti = subi;
}
}
return {bestd, besti};
}
vector<bool> vis;
int verify(int u, int fa, int fb, int p = -1) {
if (p == fa && u == fb)
return 0;
if (u == fa && p == fb)
return 0;
if (vis[u])
return 0;
vis[u] = 1;
int sz = 1;
for (int v : adj[u])
sz += verify(v, fa, fb, u);
for (auto [a, b] : ans)
if (u == a)
sz += verify(b, fa, fb, u);
else if (u == b)
sz += verify(a, fa, fb, u);
return sz;
}
int main() {
int k;
cin >> k;
adj.resize(k);
vector<pair<int, int>> edg;
for (int i = 0; i < k - 1; i++) {
int a, b;
cin >> a >> b;
a--;
b--;
adj[a].push_back(b);
adj[b].push_back(a);
edg.push_back({a, b});
}
vector<int> leafs;
is_leaf.resize(k);
for (int i = 0; i < k; i++)
if (adj[i].size() <= 1) {
leafs.push_back(i);
is_leaf[i] = 1;
}
for (int i = 0; i < leafs.size() / 2; i++) {
int best_dist = -1;
int best_leaf = -1, best_other = -1;
for (int leaf : leafs)
if (is_leaf[leaf]) {
auto [dist, other] = dfs(leaf);
if (best_dist < dist) {
best_dist = dist;
best_leaf = leaf;
best_other = other;
}
}
is_leaf[best_leaf] = 0;
is_leaf[best_other] = 0;
ans.push_back({best_leaf, best_other});
}
if (leafs.size() % 2 == 1) {
int extra_leaf = -1;
int other_leaf = 0;
for (int i = 0; i < leafs.size(); i++)
if (is_leaf[leafs[i]])
extra_leaf = leafs[i];
else
other_leaf = leafs[i];
ans.push_back({other_leaf, extra_leaf});
}
cout << ans.size() << "\n";
for (auto [a, b] : ans) {
cout << a + 1 << " " << b + 1 << "\n";
}
// TODO: remove
if (false) {
for (auto [a, b] : edg) {
vis.resize(k);
fill(vis.begin(), vis.end(), false);
if (verify(0, a, b) != k) {
cerr << "BAD" << endl;
return 1;
}
}
}
return 0;
}
