#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define ar array
void solve() {
int n;
cin >> n;
vector<vector<int>> adj(n + 1);
vector<int>leaf;
for (int i = 0; i < n - 1;i++) {
int u,v;
cin>> u >> v;
adj[u].push_back(v);
adj[v].push_back(u);
}
int r = 1;
for (int i = 1; i <= n;i++) {
if (adj[i].size() != 1) {
r = i;
}
}
function<void(int,int)> dfs = [&](int u,int p) {
if (adj[u].size() == 1 && adj[u][0] == p) {
leaf.push_back(u);
}
for (int v : adj[u]) {
if (v != p) dfs(v,u);
}
};
dfs(r,r);
cout << ((int)leaf.size() + 1) / 2 << "\n";
for (int i = 0; i < leaf.size() / 2;i++) {
cout << leaf[i] << " " << leaf[(int)leaf.size() - i - 1] << "\n";
}
if (leaf.size() % 2) cout << r << " " << leaf[leaf.size() / 2] << "\n";
}
signed main() {
ios_base::sync_with_stdio(false);
cin.tie(nullptr);
cout.tie(nullptr);
int t = 1;
//cin >> t;
while (t--) {
solve();
cout << "\n";
}
return 0;
}
