/*
Code for problem net by cookiedoth
Generated 24 Oct 2019 at 05.47 P
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# # _ _ \ \
# # (_) (_) / ;
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^_^
~_^
*/
#include <iostream>
#include <fstream>
#include <vector>
#include <set>
#include <map>
#include <bitset>
#include <algorithm>
#include <iomanip>
#include <cmath>
#include <ctime>
#include <functional>
#include <unordered_set>
#include <unordered_map>
#include <string>
#include <queue>
#include <deque>
#include <stack>
#include <complex>
#include <cassert>
#include <random>
#include <cstring>
#include <numeric>
#define ll long long
#define ld long double
#define null NULL
#define all(a) a.begin(), a.end()
#define debug(a) cerr << #a << " = " << a << endl
#define forn(i, n) for (int i = 0; i < n; ++i)
#define sz(a) (int)a.size()
using namespace std;
template<class T> int chkmax(T &a, T b) {
if (b > a) {
a = b;
return 1;
}
return 0;
}
template<class T> int chkmin(T &a, T b) {
if (b < a) {
a = b;
return 1;
}
return 0;
}
template<class iterator> void output(iterator begin, iterator end, ostream& out = cerr) {
while (begin != end) {
out << (*begin) << " ";
begin++;
}
out << endl;
}
template<class T> void output(T x, ostream& out = cerr) {
output(x.begin(), x.end(), out);
}
void fast_io() {
ios_base::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
}
const int mx = 5e5 + 228;
int n, root, deg[mx], sz[mx];
vector<vector<int> > g;
void calc_sz(int v, int pv) {
for (auto v1 : g[v]) {
if (v1 != pv) {
calc_sz(v1, v);
sz[v] += sz[v1];
}
}
sz[v] += (deg[v] == 1);
}
int find_leaf_centroid(int v, int pv) {
for (auto v1 : g[v]) {
if (v1 != pv && 2 * sz[v1] > sz[root] + 1) {
return find_leaf_centroid(v1, v);
}
}
return v;
}
void find_leaves(int v, int pv, vector<int> &res) {
// cerr << "find_leaves " << v << " " << pv << endl;
if (deg[v] == 1) {
res.push_back(v);
}
for (auto v1 : g[v]) {
if (v1 != pv) {
find_leaves(v1, v, res);
}
}
}
set<pair<int, int> > s;
vector<vector<int> > a;
void pop_back(pair<int, int> pp) {
s.erase(pp);
pp.first--;
s.insert(pp);
a[pp.second].pop_back();
}
void solve() {
root = -1;
for (int i = 0; i < n; ++i) {
if (deg[i] > 1) {
root = i;
}
}
calc_sz(root, root);
int c = find_leaf_centroid(root, root);
assert(deg[c] > 1);
// cerr << "c = " << c << endl;
int all_leaves = 0;
for (int i = 0; i < g[c].size(); ++i) {
int v = g[c][i];
vector<int> cur;
find_leaves(v, c, cur);
// cerr << "cur" << endl;
// output(all(cur));
a.push_back(cur);
all_leaves += cur.size();
s.insert({cur.size(), i});
}
vector<pair<int, int> > ans;
for (int i = 0; i < (all_leaves + 1) / 2; ++i) {
int id1 = prev(s.end())->second, id2 = prev(prev(s.end()))->second;
// cerr << "id " << id1 << " " << id2 << endl;
ans.emplace_back(a[id1].back(), a[id2].back());
pair<int, int> pp1 = (*prev(s.end())), pp2 = (*prev(prev(s.end())));
pop_back(pp1);
if (!(i == 0 && all_leaves % 2)) {
pop_back(pp2);
}
}
cout << ans.size() << "\n";
for (auto pp : ans) {
cout << pp.first + 1 << " " << pp.second + 1 << "\n";
}
}
signed main() {
fast_io();
cin >> n;
g.resize(n);
for (int i = 0; i < n - 1; ++i) {
int u, v;
cin >> u >> v;
u--;
v--;
g[u].push_back(v);
g[v].push_back(u);
deg[u]++;
deg[v]++;
}
solve();
}
