#include <cmath>
#include <cstdio>
#include <vector>
#include <iostream>
#include <algorithm>
#include <utility>
#include <queue>
#include <map>
#include <iomanip>
using namespace std;
void dfs(vector<int>&nodos,vector<vector<int> >&g,int & con,int actu,vector<bool>&v){
v[actu]=true;
if(g[actu].size()==1){
nodos.push_back(actu);
con++;
}
for(int c:g[actu]){
if(!v[c]){
dfs(nodos,g,con,c,v);
}
}
}
int main(){
ios::sync_with_stdio(false);
cin.tie(NULL);
int n,a,b;
cin>>n;
vector<vector<int> >g(n);
for(int i=0;i<n-1;i++){
cin>>a>>b;
a--;
b--;
g[a].push_back(b);
g[b].push_back(a);
}
vector<bool>v(n,false);
vector<int>nodos;
int con=0;
dfs(nodos,g,con,0,v);
if(con&1){
cout<<con/2+1<<"\n";
}
else{
cout<<con/2<<"\n";
}
for(int i=0;i<con/2;i++){
cout<<nodos[i]+1<<" "<<nodos[i+(con+1)/2]+1<<"\n";
}
if(con&1){
cout<<nodos[con/2]+1<<" ";
int p=g[con/2][0];
for(int i=0;i<n;i++){
if(i!=p && i!=nodos[con/2]){
cout<<i+1<<"\n";
break;
}
}
}
return 0;
}
