//#pragma GCC optomize("Ofast")
#pragma GCC optimize("unroll-loops")
//#pragma GCC optimize("O3")
//#pragma GCC target("avx2")
//#pragma GCC target("sse,sse2,sse4.1,sse4.2")
#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
#define max_heap priority_queue<pair <ll, pair <ll, ll>>>
#define min_heap priority_queue<pair <ll, ll>, vector<pair <ll, ll>>, greater<pair <ll, ll>>>
#define sariE cin.tie(NULL); cout.tie(NULL); ios_base::sync_with_stdio(false);
#define filE freopen("in.txt", "r", stdin); freopen("out1.txt", "w", stdout);
#define endl '\n'
#define md(a) (a % mod + mod) % mod
#define pb push_back
//mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
//cout << setprecision(5) << fixed << f;
//hash prime = 769
ll const maxn = 2e5 + 123;
ll const inf = 2e18;
ll const loG = 23;
ll const mod = 1e9 + 7;
//ll const mod = 998244353;
ll const sq = 500;
ll power(ll a, ll b, ll mod){if(b==0)return 1;if(b==1)return a;ll x = power(a, b / 2, mod);return (((x * x) % mod) * (b % 2 ? a : 1)) % mod;}
ll n, st[maxn], tim;
vector <ll> g[maxn], arr;
vector <pair <ll, ll>> ans;
void dfs(ll v, ll p){
st[v] = ++tim;
for (ll u : g[v]){
if (u != p)
dfs(u, v);
}
}
bool cmp(ll v, ll u){
return st[v] < st[u];
}
void Solve(){
cin >> n;
for (int i = 1; i < n; i++){
ll a, b; cin >> a >> b;
g[a].pb(b);
g[b].pb(a);
}
for (int i = 1; i < n + 1; i++){
if (g[i].size() == 1){
arr.pb(i);
}
}
dfs(1, 1);
sort(arr.begin(), arr.end(), cmp);
ll sz = arr.size();
for (int i = 0; i < sz / 2; i++){
ans.pb({arr[i], arr[i + (sz + 1) / 2]});
}
if (sz % 2)
ans.pb({1, arr[sz / 2]});
// for (ll x : arr)
// cout << x << ' ';
// cout << endl;
cout << (sz + 1) / 2 << endl;
for (auto p : ans)
cout << p.first << ' ' << p.second << endl;
}
int main(){
sariE;// filE;
int test = 1;
//cin >> test;
while (test--) Solve();
return 0;
}
