#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define ull unsigned long long
#define pb(e) push_back(e)
#define sv(a) sort(a.begin(),a.end())
#define sa(a,n) sort(a,a+n)
#define mp(a,b) make_pair(a,b)
#define vf first
#define vs second
#define ar array
#define all(x) x.begin(),x.end()
const int inf = 0x3f3f3f3f;
const int mod = 1000000007;
const double PI=3.14159265358979323846264338327950288419716939937510582097494459230;
bool remender(ll a , ll b){return a%b;}
const int N = 500002;
int root;
vector<int> adj[N];
bool vis[N];
vector<pair<int,int>> v;
vector<int> y;
vector<int> dfs(int node){
vis[node] = 1;
if(adj[node].size() == 1){
return {node};
}
vector<int> x,z;
for(int i : adj[node]){
if(!vis[i]){
y.clear();
y = dfs(i);
x.pb(y[0]);
if(y.size() == 2)z.pb(y[1]);
}
}
for(int i : z)x.pb(i);
z.clear();
if(x.size() % 2 == 1){
for(int i = 1; i < (int)x.size(); i+=2){
v.pb(mp(x[i] , x[i + 1]));
}
if(node != root)return {x[0]};
else {
return {x[0] , x[1]};
}
}
else {
for(int i = 2; i < (int)x.size(); i+=2){
v.pb(mp(x[i] , x[i + 1]));
}
return {x[0] , x[1]};
}
}
void solve(){
int n;
cin >> n;
for(int i = 1; i< n; i++){
int a , b;
cin >> a >> b;
adj[a].pb(b);
adj[b].pb(a);
}
for(int i = 1; i <= n; i++){
if(adj[i].size() > 1)root = i;
}
vector<int> x = dfs(root);
v.pb(mp(x[0] , x[1]));
cout << v.size() << '\n';
for(pair<int,int> p : v){
cout << p.vf << ' ' << p.vs << '\n';
}
}
int main(){
ios_base::sync_with_stdio(false);
cin.tie(NULL);
//int t;cin >> t;while(t--)
solve();
return 0;
}
