#include <bits/stdc++.h>
using namespace std;
int main() {
ios::sync_with_stdio(false);
cin.tie(nullptr);
int n;
if (!(cin >> n)) return 0;
vector<vector<int>> adj(n+1);
for (int i = 0; i < n-1; ++i) {
int a,b; cin >> a >> b;
adj[a].push_back(b);
adj[b].push_back(a);
}
vector<int> leaves;
for (int v = 1; v <= n; ++v) {
if ((int)adj[v].size() == 1) leaves.push_back(v);
}
int L = (int)leaves.size();
int k = (L + 1) / 2; // ceil(L/2)
cout << k << '\n';
// pair symmetric leaves from ends; if odd, connect middle with leaves[0]
for (int i = 0; i < L/2; ++i) {
cout << leaves[i] << ' ' << leaves[L-1-i] << '\n';
}
if (L % 2 == 1) {
cout << leaves[L/2] << ' ' << leaves[0] << '\n';
}
return 0;
}
