#include<bits/stdc++.h>
#include<string.h>
#include <algorithm>
#include <iterator>
#include <set>
#include <stdlib.h>
#define ll long long
#define fr first
#define sc second
#define pb push_back
#define YES cout<<"YES"<<endl
#define NO cout<<"NO"<<endl
#define endl "\n"
using namespace std;
ll a,b,c,d,e,f,m,i,j,n,h,g,mid,l,r,ka,dp[1000005],t[205005],q[200005],k[200105];
map<ll,ll> mee,see;
map<ll,ll> mii,maa;
vector<ll> vas[200005],ves[200005],vis,vii;
string x,y,z,te,to;
pair<ll,string> wefe;
stack<ll> munkh;
multiset<ll> mul;
int main(){
cin>>a;
for(i=1 ; i<=a-1 ; i++){
cin>>k[i]>>t[i];
vas[k[i]].pb(t[i]);
vas[t[i]].pb(k[i]);
}
for(i=1 ; i<=a ; i++){
if(vas[i].size()>1){
g=i;
break;
}
}
q[0]=g;
maa[g]=1;
l=0;
r=1;
for(i=0 ; i<vas[q[l]].size() ; i++){
if(maa[vas[q[l]][i]]==0){
q[r]=vas[q[l]][i];
maa[vas[q[l]][i]]=r;
r++;
}
}
g=r-1;
l++;
while(l<r){
for(i=0 ; i<vas[q[l]].size() ; i++){
if(maa[vas[q[l]][i]]==0){
q[r]=vas[q[l]][i];
r++;
maa[vas[q[l]][i]]=maa[q[l]];
}
}
l++;
}
m=0;
for(i=1 ; i<=a ; i++){
if(vas[i].size()==1){
ves[maa[i]].pb(i);
m++;
}
}
cout<<(m+1)/2<<endl;
h=-1;
for(i=1 ; i<=g ; i++){
if(ves[i].size()>1){
h=i;
break;
}
}
if(g%2==1){
for(i=1 ; i<g-2 ; i+=2){
cout<<ves[i][0]<<" "<<ves[i+1][0]<<endl;
}
if(h!=g){
cout<<ves[g-2][0]<<" "<<ves[g-1][0]<<endl;
cout<<ves[g][0]<<" "<<ves[h][1]<<endl;
}
else{
cout<<ves[g][0]<<" "<<ves[g-1][0]<<endl;
cout<<ves[g][1]<<" "<<ves[g-2][0]<<endl;
}
}
else{
for(i=1 ; i<g ; i+=2){
cout<<ves[i][0]<<" "<<ves[i+1][0]<<endl;
}
h=-1;
}
for(i=1 ; i<=g ; i++){
if(i==h){
j=2;
}
else{
j=1;
}
for(j=j; j<ves[i].size() ; j++){
vis.pb(ves[i][j]);
}
}
for(i=0 ; i<vis.size()-1 ; i+=2){
cout<<vis[i]<<' '<<vis[i+1]<<endl;
}
if(vis.size()%2==1){
cout<<vis[vis.size()-1]<<" "<<ves[1][0]<<endl;
}
}
