#include <bits/stdc++.h>
using namespace std;
const int N = 200005;
vector<int> g[N];
int deg[N];
int main() {
ios::sync_with_stdio(false);
cin.tie(NULL);
int n;
cin >> n;
for (int i = 1; i < n; i++) {
int u,v;
cin >> u >> v;
g[u].push_back(v);
g[v].push_back(u);
deg[u]++;
deg[v]++;
}
vector<int> leaf;
for (int i = 1; i <= n; i++)
if (deg[i] == 1)
leaf.push_back(i);
int L = leaf.size();
int k = (L + 1) / 2;
cout << k << "\n";
for (int i = 0; i < k; i++) {
cout << leaf[i] << " " << leaf[(i + k) % L] << "\n";
}
}
