#include <bits/stdc++.h>
using namespace std;
typedef int64_t llo;
#define mp make_pair
#define pb push_back
#define a first
#define b second
int n;
vector<int> adj[500001];
int co=0;
vector<int> kk;
void dfs(int no,int par=-1){
vector<pair<int,int>> ss[2];
for(auto j:adj[no]){
if(j!=par){
dfs(j,no);
/*cout<<j<<','<<x[0]<<","<<x[1]<<endl;
if(x.size()==1){
ss[0].pb({x[0],-1});
}
else{
ss[1].pb({x[0],x[1]});
}*/
}
}
if(adj[no].size()==1){
co+=1;
kk.pb(no);
}
/* if(no==3){
cout<<','<<ss[1].size()<<","<<ss[0].size()<<endl;
}
if(ss[1].size()%2==0){
for(int i=0;i<(int)(ss[1].size());i+=2){
ans.pb({ss[1][i].a,ss[1][i+1].a});
ans.pb({ss[1][i].b,ss[1][i+1].b});
}
if(ss[0].size()==0){
pair<int,int> x=ans.back();
ans.pop_back();
return {x.a,x.b};
}
for(int i=0;i<(int)(ss[0].size())-1;i+=2){
ans.pb({ss[0][i].a,ss[0][i+1].a});
}
if(ss[0].size()%2==0){
ans.pop_back();
return {ss[0].back().a,ss[0][ss[0].size()-2].a};
}
else{
return {ss[0].back().a};
}
}
else{
for(int i=0;i<(int)(ss[1].size())-1;i+=2){
ans.pb({ss[1][i].a,ss[1][i+1].a});
ans.pb({ss[1][i].b,ss[1][i+1].b});
}
for(int i=0;i<(int)(ss[0].size())-1;i+=2){
ans.pb({ss[0][i].a,ss[0][i+1].a});
}
if(ss[0].size()%2==0){
return {ss[1].back().a,ss[1].back().b};
}
else{
ans.pb({ss[1].back().a,ss[0].back().a});
return {ss[1].back().b};
}
}
*/
}
int main(){
ios_base::sync_with_stdio(false);
cin.tie(NULL);
cin>>n;
for(int i=0;i<n-1;i++){
int aa,bb;
cin>>aa>>bb;
adj[aa-1].pb(bb-1);
adj[bb-1].pb(aa-1);
}
int r=0;
for(int i=0;i<n;i++){
if(adj[i].size()>1){
r=i;
}
}
dfs(r);
cout<<(co+1)/2<<endl;
for(int i=0;i<(co+1)/2;i++){
// cout<<i<<endl;
cout<<kk[i]+1<<" "<<kk[i+co/2]+1<<endl;
}
/* for(int i=0;i<kk.size()/2;i++){
cout<<kk[i]+1<<" "<<kk[kk.size()-i-1]+1<<endl;
}
if(kk.size()%2==1){
cout<<kk[kk.size()/2]+1<<" "<<r+1<<endl;
}*/
return 0;
}
