#include<bits/stdc++.h>
typedef int ll;
#define pii pair<ll, ll>
#define fi first
#define se second
#define endl '\n'
#define TASK ""
#define N 500005
#define LOG 17
using namespace std;
const ll inf = 1e9;
bool ghuy4g;
ll n, r, in[N], out[N], timeDfs, tour[N], sola, sz[N];
vector<ll> adj[N];
vector<ll> la;
bool is[N];
set<ll> s;
void dfs(ll u, ll parent) {
in[u] = ++ timeDfs;
tour[timeDfs] = u;
for (auto v : adj[u]) {
if (v == parent) continue;
dfs(v, u);
sz[u] += sz[v];
}
if (adj[u].size() == 1) {
la.push_back(u);
is[u] = 1;
s.insert(in[u]);
sola ++ ;
sz[u] = 1;
}
out[u] = timeDfs;
}
vector<pii> res;
ll need[N], first;
void dfs2(ll u, ll parent) {
vector<ll> vt, vt_la;
for (auto v : adj[u]) {
if (v == parent) continue;
dfs2(v, u);
if (need[v]) {
vt.push_back(need[v]);
}
else {
vt_la.push_back(v);
}
}
if (is[u]) return;
if (vt.size() % 2 == 0) {
ll limit = vt.size();
if (sz[u] == vt.size()) {
limit -= 2;
}
pii quay = {0, 0};
for (int i = 0; i < limit; i += 2) {
ll x = vt[i], y = vt[i + 1];
s.erase(in[x]);
s.erase(in[y]);
first = x;
res.push_back({x, y});
quay = {x, y};
}
auto it = s.lower_bound(in[u]);
if (it == s.end()) {
//cout << "ngu";
exit(4);
}
ll x = *it;
if (!(in[u] <= x && x <= out[u])) {
/*cout << "ngu " << u << " " << tour[x] << endl;
cout << vt.size() << " "<< sz[u] << endl;
exit(3);*/
if (quay.fi == 0) {
exit(3);
}
res.pop_back();
s.insert(in[quay.fi]);
s.insert(in[quay.se]);
x = in[quay.fi];
}
x = tour[x];
need[u] = x;
//cout << "case 1 " << u << " " << need[u] << endl;
}
else {
for (int i = 0; i < vt.size(); i += 2) {
if (i == vt.size() - 1){
if (u == r) {
if (vt_la.size() == 0) {
//cout << "ngu";
exit(2);
}
res.push_back({vt[i], vt_la.back()});
s.erase(in[vt[i]]);
s.erase(in[vt_la.back()]);
first = vt[i];
break;
}
need[u] = vt[i];
//cout << "chi co 1 la => " << u << " need " << need[u] << endl;
break;
}
ll x = vt[i], y = vt[i + 1];
s.erase(in[x]);
s.erase(in[y]);
first = x;
res.push_back({x, y});
}
}
}
void solve() {
//r = 4;
//cout << "r " << r << endl;
dfs(r, r);
dfs2(r, r);
vector<ll> left;
for (auto it : s) left.push_back(tour[it]);
//cout << "left: ";
for (auto it : left) //cout << it << " ";
//cout << endl;
for (auto it : res) {
//cout << it.fi << " " << it.se << endl;
}
if (left.size() == 1) {
res.push_back({first, left[0]});
}
else {
for (int i = 0; i < left.size(); i += 2) {
if (left.size() % 2 == 1 && i == left.size() - 1) {
//cout << "la thua " << left[i - 1] << " " << left[i] << endl;
res.push_back({left[i - 1], left[i]});
break;
}
//cout << left[i] << " " << left[i + 1] << endl;
res.push_back({left[i], left[i + 1]});
}
}
cout << res.size() << endl;// << " == " << (sola + 1) / 2 << endl;
for (auto it : res) {
cout << it.fi << " " << it.se << endl;
}
}
bool klinh;
signed main() {
// freopen("test.inp", "r", stdin);
//freopen("test.out", "w", stdout);
//srand(time(0));
ios_base::sync_with_stdio(0);
cin.tie(0);
cin >> n;
for (int i = 1; i <= n - 1; i ++) {
ll u, v;
cin >> u >> v;
adj[u].push_back(v);
adj[v].push_back(u);
}
for (int i = 1; i <= n; i ++) {
if (adj[i].size() > 1) {
r = i;
break;
}
}
solve();
cerr << fabs(&klinh - &ghuy4g) / double(1024 * 1024);
}
