#include <bits/stdc++.h>
#define pii pair<int,int>
using namespace std;
int const MAX=5e5+5;
int n;
vector<int>tree[MAX];
vector<pii>rasp;
int root;
void read(){
cin>>n;
int i;
for(i=1;i<n;++i){
int u,v;
cin>>u>>v;
tree[u].push_back(v);
tree[v].push_back(u);
}
}
pii dfs(int nod,int tata){
if(tree[nod].size()==1)
return {nod,0};
vector<int>solo;
vector<pii>duo;
for(auto fiu : tree[nod])
if(fiu!=tata){
auto per=dfs(fiu,nod);
if(per.second==0)
solo.push_back(per.first);
else
duo.push_back(per);
}
int i;
if(duo.size()>1){
for(i=0;i<(int)duo.size()-1;++i)
rasp.push_back({duo[i].second,duo[i+1].first});
rasp.push_back({duo[0].first,duo.back().second});
duo.clear();
}
if(duo.size()==1){
if(solo.size()==1){
swap(solo[0],duo[0].first);
rasp.push_back(duo[0]);
duo.clear();
}
else
if(solo.size()>1){
rasp.push_back({duo[0].second,solo.back()});
solo.pop_back();
rasp.push_back({duo[0].first,solo.back()});
solo.pop_back();
duo.clear();
}
}
while(solo.size()>=2){
int nod1=solo.back();
solo.pop_back();
int nod2=solo.back();
solo.pop_back();
rasp.push_back({nod1,nod2});
}
if(nod==root){
if(solo.size()==1){
rasp.push_back({solo[0],root});
solo.clear();
}
return {0,0};
}
else{
if(solo.size()==1)
return {solo[0],0};
if(duo.size()==1)
return duo[0];
auto per=rasp.back();
rasp.pop_back();
return per;
}
}
void write(){
cout<<rasp.size()<<'\n';
for(auto [u,v] : rasp)
cout<<u<<' '<<v<<'\n';
}
void find_root(){
int i;
for(i=1;i<=n;++i)
if(tree[i].size()>1)
root=i;
}
int main()
{
read();
find_root();
dfs(root,0);
write();
return 0;
}
