#include<bits/stdc++.h>
using namespace std;
#define ll long long
#define pb push_back
ll a,i,j,g,l,r,h;
ll t[205005], q[200005], k[200105];
map<ll,ll> maa;
vector<ll> vas[200005], ves[200005], vis;
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]);
}
// find non-leaf root
for(i=1 ; i<=a ; i++){
if(vas[i].size()>1){
g=i;
break;
}
}
// BFS
q[0]=g;
maa[g]=1;
l=0;
r=1;
while(l<r){
for(ll v : vas[q[l]]){
if(maa[v]==0){
q[r]=v;
maa[v]=maa[q[l]];
r++;
}
}
l++;
}
g = r-1;
ll m=0;
// collect leaves
for(i=1 ; i<=a ; i++){
if(vas[i].size()==1){
ves[maa[i]].pb(i);
m++;
}
}
cout<<(m+1)/2<<"\n";
// find group with >=2 leaves
h=-1;
for(i=1 ; i<=g ; i++){
if(ves[i].size()>1){
h=i;
break;
}
}
// safe pairing
if(g%2==1){
for(i=1 ; i<g-2 ; i+=2){
if(!ves[i].empty() && !ves[i+1].empty())
cout<<ves[i][0]<<" "<<ves[i+1][0]<<"\n";
}
if(g>=3){
if(!ves[g-2].empty() && !ves[g-1].empty())
cout<<ves[g-2][0]<<" "<<ves[g-1][0]<<"\n";
}
if(h==-1){
if(!ves[g].empty() && !ves[1].empty())
cout<<ves[g][0]<<" "<<ves[1][0]<<"\n";
}
else{
if(ves[g].size()>0 && ves[h].size()>1)
cout<<ves[g][0]<<" "<<ves[h][1]<<"\n";
}
}
else{
for(i=1 ; i<g ; i+=2){
if(!ves[i].empty() && !ves[i+1].empty())
cout<<ves[i][0]<<" "<<ves[i+1][0]<<"\n";
}
h=-1;
}
// collect remaining leaves
for(i=1 ; i<=g ; i++){
int start = (i==h ? 2 : 1);
for(j=start; j<ves[i].size() ; j++){
vis.pb(ves[i][j]);
}
}
// pair remaining
for(i=0 ; i+1<vis.size() ; i+=2){
cout<<vis[i]<<" "<<vis[i+1]<<"\n";
}
if(vis.size()%2==1){
if(!ves[1].empty())
cout<<vis.back()<<" "<<ves[1][0]<<"\n";
}
}
