#include <iostream>
#include <vector>
using namespace std;
int main() {
int n;
cin >> n;
vector<vector<int>> graph(n + 1);
for (int i = 0; i < n - 1; ++i) {
int u, v;
cin >> u >> v;
graph[u].push_back(v);
graph[v].push_back(u);
}
// Find leaves (nodes with degree 1)
vector<int> leaves;
for (int i = 1; i <= n; ++i) {
if (graph[i].size() == 1) {
leaves.push_back(i);
}
}
vector<pair<int, int>> result;
// Pair up leaves
for (size_t i = 0; i + 1 < leaves.size(); i += 2) {
result.emplace_back(leaves[i], leaves[i + 1]);
}
// If odd number of leaves, connect the last one to the root (or any node with degree > 1)
if (leaves.size() % 2 == 1) {
for (int i = 1; i <= n; ++i) {
if (graph[i].size() > 1) {
result.emplace_back(leaves.back(), i);
break;
}
}
}
// Output
cout << result.size() << endl;
for (auto [u, v] : result) {
cout << u << " " << v << endl;
}
return 0;
}
