#include <bits/stdc++.h>
#include <ext/pb_ds/tree_policy.hpp>
#include <ext/pb_ds/assoc_container.hpp>
using namespace std;
using namespace __gnu_pbds;
template <class T> using Tree = tree<T, null_type, less<T>, rb_tree_tag,tree_order_statistics_node_update>;
#define ll long long
#define F first
#define S second
#define pb push_back
#define md ((b + e) >> 1)
const ll N = 5e5 + 5;
const ll LOG = 17;
const ll INF = 1e9 + 5;
const ll MOD = 1e9 + 7;
/*int n, m;
char mat[N][N];
pair <int, int> L[N][N], R[N][N];
pair <int, int> U[N][N], D[N][N];
pair <int, int> dir[4] = {{1, 0}, {0, 1}, {-1, 0}, {0, -1}};
vector < pair <int, int> > g[N][N];
pair <int, int> st, en;
inline bool valid(int x, int y){
return (1 <= x && x <= n && 1 <= y && y <= m && mat[x][y] == '.');;
}
inline void pre(){
for (int i = 1; i <= n; i ++){
for (int j = 1; j <= m; j ++){
if (mat[i][j] == '#'){
L[i][j] = {i, j};
U[i][j] = {i, j};
}
else {
L[i][j] = L[i][j - 1];
U[i][j] = U[i - 1][j];
}
}
}
for (int i = n; i >= 1; i --){
for (int j = m; j >= 1; j --){
if (mat[i][j] == '#'){
R[i][j] = {i, j};
D[i][j] = {i, j};
}
else {
R[i][j] = R[i][j + 1];
D[i][j] = D[i + 1][j];
}
}
}
return;
}
int dis[N][N];
queue < pair <int, int> > q;
inline void bfs(){
for (int i = 1; i <= n; i ++){
for (int j = 1; j <= m; j ++){
dis[i][j] = INF;
}
}
q.push({st.F, st.S});
while (q.size()){
auto v = q.front();
for (auto u : g[v.F][v.S]){
if (dis[v.F][v.S] + 1 < dis[u.F][u.S]){
dis[u.F][u.S] = dis[v.F][v.S] + 1;
q.push(u);
}
}
}
cout << dis[en.F][en.S] << '\n';
return;
}*/
int n;
int tim;
vector <int> g[N];
vector < pair <int, int> > leaf;
int root = 1;
void dfs(int v, int par = 0){
tim ++;
if ((int)g[v].size() == 1){
leaf.pb({tim, v});
}
for (int u : g[v]){
if (u != par){
dfs(u, v);
}
}
return;
}
int main() {
ios_base::sync_with_stdio(0), cin.tie(0), cout.tie(0);
cin >> n;
for (int i = 0; i < n - 1; i ++){
int u, v;
cin >> u >> v;
g[u].pb(v); g[v].pb(u);
}
root = 1;
while ((int)g[root].size() == 1){
root ++;
}
dfs(root);
sort(leaf.begin(), leaf.end());
int ans = ((int)leaf.size() + 1) / 2;
int nim = (int)leaf.size() / 2;
cout << ans << '\n';
for (int i = nim; i < (int)leaf.size(); i ++){
cout << leaf[i - nim].S << ' ' << leaf[i].S << '\n';
}
/*cin >> n >> m;
for (int i = 1; i <= n; i ++){
for (int j = 1; j <= m; j ++){
cin >> mat[i][j];
if (mat[i][j] == 's'){
st = {i, j};
mat[i][j] = '.';
}
if (mat[i][j] == 'c'){
en = {i, j};
mat[i][j] = '.';
}
}
}
pre();
for (int i = 1; i <= n; i ++){
for (int j = 1; j <= m; j ++){
for (int d = 0; d < 4; d ++){
int x = i + dir[d].F;
int y = j + dir[d].S;
if (valid(x, y)){
g[i][j].pb({x, y});
g[x][y].pb({i, j};
}
}
}
}
bfs();*/
return 0;
}
