#include <bits/stdc++.h>
/*
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
*/
using namespace std;
// using namespace __gnu_pbds;
using namespace chrono;
// mt19937 rng((int) std::chrono::steady_clock::now().time_since_epoch().count());
/*
template <class T> using ordered_set = tree <T, null_type, less <T>, rb_tree_tag, tree_order_statistics_node_update>;
*/
//***************** CONSTANTS *****************
const int MXN = 500'000;
//***************** GLOBAL VARIABLES *****************
vector<int> g[MXN], leaves;
//***************** AUXILIARY STRUCTS *****************
//***************** MAIN BODY *****************
void dfs(int node, int p){
if(g[node].size() == 1) leaves.push_back(node + 1);
for(int v : g[node]) if(v != p) dfs(v, node);
}
void solve(){
int N;
cin >> N;
for(int i = 0; i < N - 1; i++){
int u, v;
cin >> u >> v;
--u, --v;
g[u].push_back(v);
g[v].push_back(u);
}
dfs(0, 0);
int c = leaves.size();
cout << (c + 1) / 2 << '\n';
for(int i = 0; i < c / 2; i++)
cout << leaves[i] << ' ' << leaves[i + c/2] << '\n';
if(c & 1) cout << leaves[0] << ' ' << leaves[c - 1] << '\n';
}
//***************** *****************
int32_t main(){
ios_base::sync_with_stdio(NULL);
cin.tie(NULL);
#ifdef LOCAL
auto begin = high_resolution_clock::now();
#endif
int tc = 1;
// cin >> tc;
for (int t = 0; t < tc; t++)
solve();
#ifdef LOCAL
auto end = high_resolution_clock::now();
cout << fixed << setprecision(4);
cout << "Execution Time: " << duration_cast<duration<double>>(end - begin).count() << "seconds" << endl;
#endif
return 0;
}
/*
If code gives a WA, check for the following :
1. I/O format
2. Are you clearing all global variables in between tests if multitests are a thing
3. Can you definitively prove the logic
*/
