#include <bits/stdc++.h>
using namespace std;
int n,m,k,q;
vector<vector<int>> adj;
vector<int> dep;
vector<pair<int,int>> v;
void dfs(int x, int i){
if(adj[x].size() == 1){
v.emplace_back(dep[x], x);
return;
}
for(auto x:adj[x]){
if(x == i) continue;
dep[x] = dep[x] + 1;
dfs(x, x);
}
}
int main(){
cin >> n;
adj.resize(n+1);
dep.resize(n+1, 0);
for(int i = 2; i <= n; i++){
int a,b;
cin >> a >> b;
adj[a].emplace_back(b);
adj[b].emplace_back(a);
}
vector<pair<int,int>> p;
int sz = INT_MAX;
for(int i = 1; i <= n; i++){
vector<pair<int,int>> ans;
vector<int> cnt;
for(auto x : adj[i]){
dep[x] = 1;
v.clear();
dfs(x, i);
sort(v.begin(), v.end(), greater<pair<int,int>>());
ans.emplace_back(i, v[0].second);
for(int j = 2; j < v.size(); j += 2)
ans.emplace_back(v[j-1].second, v[j].second);
if(v.size() % 2 == 0)
cnt.emplace_back(v.back().second);
}
for(int k = 1; k < cnt.size(); k += 2)
ans.emplace_back(cnt[k-1], cnt[k]);
if(cnt.size() % 2 == 1)
ans.emplace_back(cnt.back(), i);
if(sz > ans.size()){
p = ans;
sz = ans.size();
}
}
cout << p.size() << '\n';
for(auto [a, b] : p){
cout << a << ' ' << b << '\n';
}
}
