#include <bits/stdc++.h>
#include <fstream>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace __gnu_pbds;
using namespace std;
template<class T> using ordered_set = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
struct custom_hash {static uint64_t splitmix64(uint64_t x) {x += 0x9e3779b97f4a7c15;x = (x ^ (x >> 30)) * 0xbf58476d1ce4e5b9;x = (x ^ (x >> 27)) * 0x94d049bb133111eb;return x ^ (x >> 31);}size_t operator()(uint64_t x) const {static const uint64_t FIXED_RANDOM = chrono::steady_clock::now().time_since_epoch().count();return splitmix64(x + FIXED_RANDOM);}};
// string __fname = ""; ifstream in (__fname + ".in"); ofstream out (__fname + ".out");
// #define cin in
// #define cout out
#define int64 long long
#define uint64 unsigned long long
#define x first
#define y second
#define pb push_back
#define pii pair <int, int>
#define pii64 pair <int64, int64>
#define db(x) cout << "> " << #x << ": " << (x) << "\n"
#define qr queries()
#define yn(x) if (x) {ctn("Yes");}else {ctn("No");}
void solve(int);
void queries(){int n;cin >> n;for (int i = 1; i <= n; i++) solve(i);}
template<class T>T ceildiv(T a, T b) {return a / b + !!(a % b);}
template<class T>T gcd (T a, T b){return (b ? gcd(b, a % b): a);}
template<class T>T lcm (T a, T b){return a * b / gcd(a, b);}
// // // // // // // // // // // // // // // // // // // // // //
/* TEMPLATE - VANILLA */
// // // // // // // // // // // // // // // // // // // // // //
const int ddx[] = {-1, -1, 0, 1, 1, 1, 0, -1};
const int ddy[] = {0, 1, 1, 1, 0, -1, -1, -1};
const int dx[] = {-1, 0, 1, 0};
const int dy[] = {0, 1, 0, -1};
const double pi = 3.14159265359;
const double eps = 1e-6;
const int64 hash_inv = 940594066;
const int64 hash_p = 101;
const int64 mod = 1e9 + 7;
const int maxn = 5e5 + 2;
vector <int> ad[maxn];
void solve(int id){
int n;
cin >> n;
for (int i = 0; i < n - 1; i++){
int a,b;
cin >> a >> b;
ad[a].push_back(b);
ad[b].push_back(a);
}
vector <int> lf;
auto dfs = [&] (auto dfs, int u, int p = -1) -> void {
// cerr << u << " " << p << "\n";
if (ad[u].size() == 1) lf.push_back(u);
for (int v: ad[u]) {
if (v == p) continue;
dfs(dfs, v, u);
}
};
dfs(dfs, 1);
int k = lf.size();
cout << (k + 1) / 2 << "\n";
for (int i = 0; i < k / 2; i++){
cout << lf[i] << " " << lf[k / 2 + i] << "\n";
}
if (k % 2) cout << lf[0] << " " << lf[k - 1] << "\n";
return;
}
int main(){
ios_base::sync_with_stdio(0); cin.tie(0); cout << fixed; cout << setprecision(10);
solve(1);
return 0;
}
