#include <algorithm>
#include <bits/stdc++.h>
#include <cassert>
using namespace std;
#define ll long long
#define ff first
#define ss second
#define ln "\n"
const ll MOD = 998244353;
const ll INF = 2e18;
void dfs(ll u, ll p, vector<vector<ll>> &A, vector<ll> &lf){
for (auto v:A[u]){
if (v==p) continue;
dfs(v, u, A, lf);
}
if (A[u].size()==1) lf.push_back(u);
}
void solve(){
ll n; cin >> n;
vector<vector<ll>> A(n);
for (ll i=0; i<n-1; i++){
ll u, v; cin >> u >> v; u--; v--;
A[u].push_back(v); A[v].push_back(u);
}
vector<ll> lf; dfs(1, 1, A, lf);
vector<pair<ll, ll>> e;
for (ll i=2; i<(ll)lf.size(); i++){
e.push_back({lf[i-2], lf[i]});
}
if (lf.size()<=3) e.push_back({lf[1], lf[0]});
cout << e.size() << ln;
for (auto ch:e) cout << ch.ff+1 << " " << ch.ss+1 << ln;
}
int main(){
ios_base::sync_with_stdio(0); cin.tie(nullptr);
ll t=1;
// cin >> t;
while (t--) solve();
}
