#include<bits/stdc++.h>
using namespace std;
int n;
vector<vector<int>> adj;
vector<int> allLeaves;
int dfs(int x, int prev){
if(adj[x].size()==1){
//cout << "x: "<< x+1<<"\n";
allLeaves.push_back(x);
return 1;
}
int cnt = 0;
for(auto u : adj[x]){
if(u==prev)continue;
//cout << "for " << x+1 << ": " << u+1 << "\n";
cnt+=dfs(u, x);
}
return cnt;
}
signed main(){
cin >> n;
adj.resize(n);
int root = 0;
for(int i = 0; i < n-1; i++){
int u, v;
cin >> u >> v; u--; v--;
adj[u].push_back(v);
adj[v].push_back(u);
if(adj[u].size()>adj[root].size()){
root = u;
}
if(adj[v].size()>adj[root].size()){
root = v;
}
}
for(int i = 0; i < adj[root].size(); i++){
//cout << "begin: " << adj[root][i] << "\n";
dfs(adj[root][i], root);
}
/*for(int i = 0; i < allLeaves.size(); i++){
cout << allLeaves[i] << "\n";
}*/
vector<pair<int, int>> ans;
for(int i = 0; i < (allLeaves.size()+(allLeaves.size()%2))/2; i++){
int connectLeave = allLeaves[(i+(allLeaves.size()+(allLeaves.size()%2))/2)%(allLeaves.size())];
ans.push_back({allLeaves[i], connectLeave});
}
cout << ans.size() << "\n";
for(auto u : ans){
cout << u.first+1 << " " << u.second+1 << "\n";
}
}
