#include "bits/stdc++.h"
using namespace std;
/*
#include <ext/pb_ds/assoc_container.hpp>
using namespace __gnu_pbds;
using ordered_set = tree<int, null_type, less<int>, rb_tree_tag, tree_order_statistics_node_update>;
*/
#define all(x) begin(x), end(x)
#define sz(x) (int)x.size()
using ll = long long;
const int mod = 1e9+7;
void solve(int tc) {
int n;
cin >> n;
vector<vector<int>> adj(n);
for (int i = 0; i < n-1; ++i) {
int u, v;
cin >> u >> v;
--u, --v;
adj[u].push_back(v);
adj[v].push_back(u);
}
vector<int> leaf;
for (int i = 0; i < n; ++i) {
if (sz(adj[i]) == 1) {
leaf.push_back(i);
}
}
cout << (sz(leaf))/2 << '\n';
for (int i = 0; i < sz(leaf)/2; ++i) {
cout << leaf[i]+1 << " " << leaf[i+sz(leaf)/2]+1 << '\n';
}
// if (sz(leaf)&1) cout << 1 << " " << leaf.back()+1 << '\n';
}
signed main() {
ios_base::sync_with_stdio(false); cin.tie(NULL);
int tc = 1;
//cin >> tc;
for (int i = 1; i <= tc; ++i) solve(i);
return 0;
}
