#include <bits/stdc++.h>
using namespace std;
#define int long long
const int inf = 1e18;
const int MAX = 1e6 + 6;
bool used[MAX];
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);
// for(int i = 1; i <= n; i++){
// if(adj[i].size() == 1)
// node.push_back(i);
// }
cout << (node.size() + 1) / 2 << endl;
srand(time(0));
for(auto i : node){
vector < int > idx;
if(used[i]) continue;
used[i] = true;
for(auto j : node){
// if(i == j) continue;
if(!used[j])
idx.push_back(j);
}
if(!idx.size()){
cout << i << ' ' << node[node.size() - 1] << endl;
continue;
}
int in = rand() % (int)idx.size();
cout << i << ' ' << idx[in] << endl;
used[idx[in]] = true;
}
}
