#include <bits/stdc++.h>
using namespace std;
vector<vector<int>> adj;
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 {besti, bestd};
}
int main() {
int k;
cin >> k;
adj.resize(k);
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);
}
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;
}
vector<pair<int, int>> ans;
int idx = 0;
for (int i = 0; i < leafs.size() / 2; i++) {
while (!is_leaf[leafs[idx]])
idx++;
auto [_, other] = dfs(leafs[idx]);
is_leaf[other] = 0;
is_leaf[leafs[idx]] = 0;
ans.push_back({leafs[idx], other});
idx++;
}
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";
}
return 0;
}
