#include <bits/stdc++.h>
using namespace std;
const int N = 5e5+10;
vector<int> leaf, adj[N];
void dfs(int u, int p){
if(adj[u].size() == 1) leaf.push_back(u);
for(int v : adj[u]){
if(v == p) continue;
dfs(v, u);
}
}
int main(){
ios_base::sync_with_stdio(false);
cin.tie(nullptr);
int n;
cin >> n;
for(int i = 1; i < n; ++i){
int u, v;
cin >> u >> v;
adj[u].push_back(v);
adj[v].push_back(u);
}
dfs(1, -1);
cout << (int(leaf.size())+1)/2 << '\n';
if(int(leaf.size())&1) leaf.push_back(leaf.front());
int l = 0, r = int(leaf.size())/2;
while(r < leaf.size()){
cout << leaf[l++] << ' ' << leaf[r++] << '\n';
}
}
