#include <bits/stdc++.h>
using namespace std;
#define int long long
const int inf = 1e18;
const int MAX = 1e6 + 6;
vector < int > node;
map < pair < int , int > , int > mp;
vector < vector < int > > adj(MAX);
void dfs(int u, int pa){
if(adj[u].size() == 1)
node.push_back(u);
for(auto v : adj[u]){
if(v == pa) continue;
dfs(v, u);
}
}
signed main(){
int n;
cin >> n;
for(int i = 1; i < n; i++){
int u, v;
cin >> u >> v;
mp[{u, v}] = 1;
mp[{v, u}] = 1;
adj[u].push_back(v);
adj[v].push_back(u);
}
dfs(1, 0);
cout << (node.size() + 1) / 2 << endl;
// for(auto i : node)
// cout << i << ' ';
// cout << endl;
for(int i = 0; i < (node.size() + 1) / 2; i++){
if(node.size() % 2 == 1 && i + 1 == (node.size() + 1) / 2){
cout << node[i] << ' ' << node[node.size() - 1] << endl;
return 0;
}
cout << node[i] << ' ' << node[i + (node.size() + 1) / 2] << endl;
}
}
