#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace std;
using namespace __gnu_pbds;
template<typename T> using Tree = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
typedef long long int ll;
typedef long double ld;
typedef pair<int,int> pii;
typedef pair<ll,ll> pll;
#define fastio ios_base::sync_with_stdio(false); cin.tie(NULL)
#define pb push_back
#define endl '\n'
#define sz(a) (int)a.size()
#define setbits(x) __builtin_popcountll(x)
#define ff first
#define ss second
#define conts continue
#define ceil2(x,y) ((x+y-1)/(y))
#define all(a) a.begin(), a.end()
#define rall(a) a.rbegin(), a.rend()
#define yes cout << "Yes" << endl
#define no cout << "No" << endl
#define rep(i,n) for(int i = 0; i < n; ++i)
#define rep1(i,n) for(int i = 1; i <= n; ++i)
#define rev(i,s,e) for(int i = s; i >= e; --i)
#define trav(i,a) for(auto &i : a)
template<typename T>
void amin(T &a, T b) {
a = min(a,b);
}
template<typename T>
void amax(T &a, T b) {
a = max(a,b);
}
#ifdef LOCAL
#include "debug.h"
#else
#define debug(x) 42
#endif
/*
*/
const int MOD = 1e9 + 7;
const int N = 5e5 + 5;
const int inf1 = int(1e9) + 5;
const ll inf2 = ll(1e18) + 5;
vector<ll> adj[N];
vector<ll> sub_leaves(N);
void dfs1(ll u, ll p){
if(sz(adj[u]) == 1){
sub_leaves[u] = 1;
}
trav(v,adj[u]){
if(v == p) conts;
dfs1(v,u);
sub_leaves[u] += sub_leaves[v];
}
}
ll dfs2(ll u, ll p, ll tot){
trav(v,adj[u]){
if(v == p) conts;
if(sub_leaves[v] > tot/2){
return dfs2(v,u,tot);
}
}
return u;
}
vector<ll> leaves[N];
void dfs3(ll u, ll p, ll r){
if(sz(adj[u]) == 1){
leaves[r].pb(u);
}
trav(v,adj[u]){
if(v == p) conts;
dfs3(v,u,r);
}
}
void solve(int test_case)
{
ll n; cin >> n;
rep1(i,n-1){
ll u,v; cin >> u >> v;
adj[u].pb(v), adj[v].pb(u);
}
ll root = -1;
rep1(i,n){
if(sz(adj[i]) >= 2){
root = i;
break;
}
}
assert(root != -1);
dfs1(root,-1);
ll c = dfs2(root,-1,sub_leaves[root]);
trav(v,adj[c]){
dfs3(v,c,v);
}
vector<pll> ans;
priority_queue<pll> pq;
trav(v,adj[c]){
pq.push({sz(leaves[v]),v});
}
while(sz(pq) >= 2){
auto [s1,u] = pq.top();
pq.pop();
auto [s2,v] = pq.top();
pq.pop();
ll x = leaves[u].back();
leaves[u].pop_back();
ll y = leaves[v].back();
leaves[v].pop_back();
ans.pb({x,y});
if(s1-1 >= 1){
pq.push({s1-1,u});
}
if(s2-1 >= 1){
pq.push({s2-1,v});
}
}
if(!pq.empty()){
auto [s1,u] = pq.top();
pq.pop();
assert(s1 == 1);
ll x = leaves[u].back();
leaves[u].pop_back();
ans.pb({c,x});
}
assert(pq.empty());
cout << sz(ans) << endl;
for(auto [u,v] : ans){
cout << u << " " << v << endl;
}
}
int main()
{
fastio;
int t = 1;
// cin >> t;
rep1(i, t) {
solve(i);
}
return 0;
}
