#include <bits/stdc++.h>
using namespace std;
vector<int> adj[500008], rem[500008];
void add_edge(int u, int v) {adj[u].push_back(v); adj[v].push_back(u);}
vector<pair<int, int>> ans;
int timer = 0;
void DFS(int u, int p) {
bool is_leaf = 1; vector<pair<int, int>> Q, Q2;
for (int v : adj[u]) if (v != p) {
DFS(v, u); is_leaf = 0;
for (int i : rem[v]) Q.emplace_back(v * (rem[v].size() == 1 ? 1 : -1), i);
}
sort(Q.begin(), Q.end());
for (pair<int, int> item : Q)
if (!Q2.empty() && Q2.back().first != item.first) {
ans.emplace_back(Q2.back().second, item.second);
Q2.pop_back();
}
else Q2.emplace_back(item);
if (is_leaf) rem[u].push_back(u);
else if (Q2.empty()) {
Q2 = {{0, ans.back().first}, {0, ans.back().second}};
ans.pop_back();
}
for (pair<int, int> p : Q2) rem[u].push_back(p.second);
Q.clear(); Q2.clear();
// cout << ">> " << u << endl;
// for (pair<int, int> p : ans) cout << p.first << ' ' << p.second << endl;
}
signed main() {
ios_base::sync_with_stdio(0);
cin.tie(0); cout.tie(0);
int n, u, v; cin >> n;
for (int i = 1; i < n; ++i) cin >> u >> v, add_edge(u, v);
if (n == 2) {
cout << 1 << '\n' << 1 << ' ' << 2;
return 0;
}
int rt = 1;
while (adj[rt].size() == 1) ++rt;
DFS(rt, 0);
while (rem[rt].size() > 1) {
ans.emplace_back(*rem[rt].rbegin(), *(rem[rt].rbegin() + 1));
rem[rt].pop_back(); rem[rt].pop_back();
}
if (!rem[rt].empty()) ans.emplace_back(rt, rem[rt][0]);
cout << ans.size() << '\n';
for (pair<int, int> p : ans) cout << p.first << ' ' << p.second << '\n';
}
