#include <bits/stdc++.h>
#define d1(x) cout << #x << " : " << x << endl << flush
#define d2(x, y) cout << #x << " : " << x << " " << #y << " : " << y << endl << flush
#define d3(x, y, z) cout << #x << " : " << x << " " << #y << " : " << y << " " << #z << " : " << z << endl << flush
#define d4(x, y, z, a) cout << #x << " : " << x << " " << #y << " : " << y << " " << #z << " : " << z << " "<< #a << " : " << a << endl << flush
#define arr(x) array <ll, x>
#define ld long double
#define ll long long
#define int long long
#define pb push_back
#define endl '\n'
#define lc v << 1
#define rc v << 1 | 1
using namespace std;
const int INF = 1e9 + 24 + (34 / 10); // 34 ---> 35
const int MAXN = 5e5 + 24 + (34 / 10); // 34 ---> 35
vector <int> adj[MAXN];
vector <arr(2)> ans;
int r;
bool cmp(vector <int> a, vector <int> b){
return a.size() > b.size();
}
void merge(vector <vector <int>> a){
while(!a.empty() && (a.back()).empty())
a.pop_back();
int n = a.size();
// for(auto x : a){
// for(auto v : x)
// cout << v + 1 << " ";
// cout << endl;
// }
// cout << endl;
for(int i = 0; i < 2 * n; i += 2){
int x = i % n, y = (i + 1) % n;
if(a[x].empty() || a[y].empty()){
i--;
continue;
}
ans.pb({a[x].back(), a[y].back()});
a[x].pop_back();
a[y].pop_back();
}
}
vector <int> dfs(int u, int p){
vector <vector <int>> child;
vector <int> res;
if(u != r && adj[u].size() == 1){
res.pb(u);
return res;
}
int cnt = 0;
for(auto v : adj[u]){
if(v != p){
child.pb(dfs(v, u));
cnt += (child.back()).size();
}
}
// d1(u + 1);
// for(auto x : child){
// for(auto v : x)
// cout << v + 1 << " ";
// cout << endl;
// }
sort(child.begin(), child.end(), cmp);
if(cnt & 1){
res.pb((child[0]).back());
(child[0]).pop_back();
}
else if(child.size() == 1){
res = child.back();
child.pop_back();
}
else{
res.pb((child[0]).back());
res.pb((child[1]).back());
(child[0]).pop_back();
(child[1]).pop_back();
}
// d1(u + 1);
// for(auto v : res)
// cout << v + 1 << " ";
// cout << endl;
sort(child.begin(), child.end(), cmp);
merge(child);
return res;
}
signed main(){
ios_base::sync_with_stdio(0);
cin.tie(0);
int n;
cin >> n;
for(int i = 1; i < n; i++){
int u, v;
cin >> u >> v;
u--;
v--;
adj[u].pb(v);
adj[v].pb(u);
}
for(int i = 0; i < n; i++)
if(adj[i].size() > 1)
r = i;
vector <int> eli = dfs(r, r);
// d1(r);
if(eli.size() == 1){
if(r != adj[eli[0]][0])
ans.pb({r, eli[0]});
else{
for(auto v : adj[r])
if(v != eli[0] && v != adj[eli[0]][0]){
ans.pb({eli[0], v});
break;
}
}
}
else
ans.pb({eli[0], eli[1]});
cout << ans.size() << endl;
for(auto [u, v] : ans)
cout << u + 1 << " " << v + 1 << endl;
}
// Ey To Bahane! :_)))
// -------------<3------------- //
/*
Magasan dor shirini:
1. MAXN
2. Input style
3. index or value? Masale In Ast!
4. MOD
*/
