#include <cstdio>
#include <stdio.h>
#include <stdbool.h>
#include <iostream>
#include <map>
#include <vector>
#include <climits>
#include <stack>
#include <string>
#include <queue>
#include <algorithm>
#include <set>
#include <unordered_set>
#include <unordered_map>
#include <cmath>
#include <cctype>
#include <bitset>
#include <iomanip>
#include <cstring>
#include <numeric>
#include <cassert>
using namespace std;
#define int long long
#define pii pair<int, int>
#define mp make_pair
#define pb push_back
#define fi first
#define se second
vector<vector<int> > graph;
vector<int> leaf;
void dfs(int node, int par){
if (graph[node].size()==1)leaf.pb(node);
for (auto num:graph[node])if (num!=par)dfs(num, node);
}
int32_t main(){
ios_base::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
int n, a, b;
cin>>n;
graph.resize(n+1);
for (int i=1; i<n; ++i){
cin>>a>>b;
graph[a].pb(b);
graph[b].pb(a);
}
dfs(1, -1);
cout<<(leaf.size()+1)/2<<"\n";
for (int i=0; i<leaf.size()/2; ++i)cout<<leaf[i]<<" "<<leaf[leaf.size()/2+i]<<"\n";
if (leaf.size()%2)cout<<leaf[0]<<" "<<leaf.back();
}
