// Born_To_Laugh - Hughie Do
#include <bits/stdc++.h>
#define alle(AC) AC.begin(), AC.end()
#define fi first
#define se second
using namespace std;
typedef long long ll;
[[maybe_unused]] const ll MOD = 998244353, INF = 1e9 + 7;
const int maxn = 5e5 + 10;
vector<int> adj[maxn];
int leafs[maxn];
int n;
int id = 0;
void dfs(int a, int par){
if(adj[a].size() == 1){
id++;
leafs[id] = a;
}
for(auto &elm: adj[a]){
if(elm == par)continue;
dfs(elm, a);
}
}
void solve(){
cin >> n;
for(int i=1; i<n; ++i){
int a, b;cin >> a >> b;
adj[a].push_back(b);
adj[b].push_back(a);
}
dfs(1, -1);
if(id & 1){
cout << (id + 1) / 2 << '\n';
}
else cout << id/2 << '\n';
for(int i=1; i<=(int)id/2; ++i){
cout << leafs[i] << ' ' << leafs[i + (int)id/2] << '\n';
}
if(id & 1){
cout << leafs[1] << ' ' << leafs[id] << '\n';
}
}
signed main(){
ios_base::sync_with_stdio(false);
cin.tie(nullptr);
solve();
}
