#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define ar array
void solve() {
int n;
cin >> n;
vector<vector<int>> adj(n + 1);
vector<vector<int>>leaf;
for (int i = 0; i < n - 1;i++) {
int u,v;
cin>> u >> v;
adj[u].push_back(v);
adj[v].push_back(u);
}
int r = 1,mn = n;
for (int i = 1; i <= n;i++) {
if (adj[i].size() != 1) {
if (adj[i].size() < mn) {
mn = adj[i].size();
r = i;
}
}
}
int cnt = 0;
leaf.resize((int)adj[r].size() + 5);
function<void(int,int)> dfs = [&](int u,int p) {
if (adj[u].size() == 1 && adj[u][0] == p) {
leaf[cnt].push_back(u);
}
for (int v : adj[u]) {
if (v != p) dfs(v,u);
}
};
int ans = 0;
for (int u : adj[r]) {
dfs(u,r);
ans += (int)leaf[cnt++].size();
}
vector<int>id(cnt);
iota(id.begin(),id.end(),0);
sort(id.begin(),id.end(),[&](int i,int j){
return (int)leaf[i].size() > (int)leaf[j].size();
});
// for (int x : id) cerr << x << " ";
// cerr << "\n";
cout << (ans + 1) / 2 << "\n";
set<ar<int,2>> st,leaves;
int cnt1= 0;
for (int i = 0; i < cnt;i++) {
if (leaf[id[i]].empty()) continue;
while (!leaf[id[i]].empty() && (ans % 2 != 1 || cnt1 != cnt - 1 || leaf[id[i]].size() != 1)) {
// cerr << id[i] << " " << leaf[id[i]].size() << "\n";
for (int j = i + 1; j < cnt && (!leaf[id[i]].empty() && (ans % 2 != 1 || cnt1 != cnt - 1 || leaf[id[i]].size() != 1));j++) {
if (leaf[id[j]].empty()) continue;
int u = leaf[id[i]].back();
int v = leaf[id[j]].back();
st.insert({min(u,v),max(u,v)});
leaves.insert({u,i});
leaves.insert({v,j});
leaf[id[i]].pop_back();
leaf[id[j]].pop_back();
if (leaf[id[i]].empty()) cnt1++;
if (leaf[id[j]].empty()) cnt1++;
}
}
}
if (ans % 2) {
int u = 0,t1 = 0;
for (int i = 0; i < cnt;i++) {
if (leaf[id[i]].size()) {
u = leaf[id[i]][0];
t1 = i;
break;
}
}
st.insert({r,u});
}
for (auto [u,v] : st) cout << u << " " << v << "\n";
}
signed main() {
ios_base::sync_with_stdio(false);
cin.tie(nullptr);
cout.tie(nullptr);
int t = 1;
//cin >> t;
while (t--) {
solve();
// cout << "\n";
}
return 0;
}
