#include <bits/stdc++.h>
using namespace std;
#define int long long
#define INF 9e18
void solve() {
int n;
cin >> n;
vector<vector<int>> adj(n);
for (int i = 1; i < n; i++) {
int u, v; cin >> u >> v; u--, v--;
adj[u].push_back(v);
adj[v].push_back(u);
}
vector<int> leaves;
for (int u = 0; u < n; u++) {
if (adj[u].size() == 1) {
leaves.push_back(u + 1);
}
}
int m = leaves.size();
cout << m / 2 + (m & 1) << "\n";
for (int i = 1; i < m; i += 2) {
cout << leaves[i - 1] << " " << leaves[i] << "\n";
}
if (m & 1) cout << leaves.back() << " " << leaves[0] << "\n";
}
signed main() {
ios_base::sync_with_stdio(0);
cin.tie(0);
solve();
return 0;
}
