#include <bits/stdc++.h>
using namespace std;
#define int long long
#define ar array
#define all(x) x.begin(), x.end()
#define sortall(x) sort(all(x))
#define rep(i,a,b) for(int i = a; i < b; i++)
#define per(i,a,b) for(int i = a; i >= b; i--)
#define trav(a,x) for(auto& a : x)
#define sz(x) (int)(x).size()
#define ff first
#define ss second
#define pb push_back
#define mp make_pair
#define endl '\n'
#define debug(x) cerr << #x << " = " << x << endl
const int N = 1e6 + 5;
struct BIT{
int n;
vector<int>ft;
void init(int _n){
n = _n;
ft.resize(n + 1);
}
void update(int x, int val){
for(; x <= n; x += x & -x){
ft[x] += val;
}
}
int query(int x){
int res = 0;
for(; x > 0; x -= x & -x){
res += ft[x];
}
return res;
}
int get(int l,int r){
return query(r) - query(l - 1);
}
};
struct DSU{
int n;
vector<int> par, siz;
void init(int _n){
n = _n + 5;
par.resize(n);
siz.resize(n);
iota(all(par), 0);
fill(all(siz), 1);
}
int find(int x){
return x == par[x] ? x : par[x] = find(par[x]);
}
void unite(int x, int y){
x = find(x);
y = find(y);
if(x != y){
if(siz[x] < siz[y]) swap(x, y);
par[y] = x;
siz[x] += siz[y];
}
}
};
vector<int>adj[N];
vector<int>indeg(N);
vector<int>v;
void dfs(int u, int p){
if(indeg[u] == 1){
v.push_back(u);
return;
}
for(auto v : adj[u]){
if(v != p){
dfs(v, u);
}
}
}
void solve(){
int n;
cin >> n;
rep(i, 0, n - 1){
int u, v;
cin >> u >> v;
adj[u].push_back(v);
adj[v].push_back(u);
indeg[u]++;
indeg[v]++;
}
rep(i, 1, n + 1){
if(indeg[i] > 1){
dfs(i, -1);
break;
}
}
int ans = sz(v);
cout << (ans + 1) / 2 << endl;
rep(i, 0, (ans + 1) / 2){
cout << v[i] << " " << v[i + (ans + 1) / 2] << endl;
}
}
signed main() {
ios::sync_with_stdio(0); cin.tie(0);
int T = 1;
while(T--){
solve();
}
}
