#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#include <bits/stdc++.h>
using namespace std;
using namespace __gnu_pbds;
typedef long long ll;
typedef long double ld;
typedef pair<int,int> pii;
typedef pair<ll,ll> pll;
typedef pair<ld,ld> pdd;
#define ff(i,a,b) for(int i = a; i <= b; i++)
#define fb(i,b,a) for(int i = b; i >= a; i--)
#define trav(a,x) for (auto& a : x)
#define sz(a) (int)(a).size()
#define pb push_back
#define fi first
#define se second
#define lb lower_bound
#define ub upper_bound
#define all(a) a.begin(), a.end()
#define rall(a) a.rbegin(), a.rend()
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
template<typename T>
using ordered_set = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
// os.order_of_key(k) the number of elements in the os less than k
// *os.find_by_order(k) print the k-th smallest number in os(0-based)
const int mod = 998244353;
const int inf = 1e9 + 5;
const int mxN = 500005;
int n;
vector<int> g[mxN];
int timer = 0;
int in[mxN];
void dfs(int v, int p){
in[v] = ++timer;
for(auto u : g[v]){
if(u != p){
dfs(u, v);
}
}
}
bool cmp(int s1, int s2){
return in[s1] < in[s2];
}
int main() {
cin.tie(0)->sync_with_stdio(0);
cin >> n;
ff(i,1,n - 1){
int u, v;
cin >> u >> v;
g[u].pb(v);
g[v].pb(u);
}
if(n == 1){
cout << 1 << '\n';
cout << 1 << " " << 1 << '\n';
return 0;
}
dfs(1, -1);
vector<int> leaf;
ff(i,1,n)if(sz(g[i]) == 1)leaf.pb(i);
sort(all(leaf), cmp);
cout << (sz(leaf) + 1) / 2 << '\n';
if(sz(leaf) % 2 == 1){
cout << leaf[0] << " " << leaf.back() << '\n';
leaf.pop_back();
}
int K = sz(leaf) / 2;
for(int i = 0; i + K < sz(leaf); i++){
cout << leaf[i] << " " << leaf[i + K] << '\n';
}
return 0;
}
/*
// probati bojenje sahovski
*/
