#include <bits/stdc++.h>
#define int long long
using namespace std;
int a;
vector <int> z[1000005];
int root;
int par[1000005];
vector <int> sz[1000005];
int k;
int find(int u){
if (par[u]==u){
return u;
}
return par[u]=find(par[u]);
}
void join(int x,int y){
x=find(x);
y=find(y);
if (x==y){
return;
}
while ( (sz[x].size()>1 || sz[y].size()>1) && sz[x].size() && sz[y].size()){
cout << sz[x].back() << " " << sz[y].back() << "\n";
sz[x].pop_back();
sz[y].pop_back();
}
par[y]=x;
while (sz[y].size()){
int p=sz[y].back();
sz[x].push_back(p);
sz[y].pop_back();
}
}
void dfs(int i,int parent){
for (auto p:z[i]){
if (p==parent){
continue;
}
dfs(p,i);
join(i,p);
}
}
signed main()
{
ios_base::sync_with_stdio(false);
cin.tie(NULL);
cin >> a;
for (int i=1;i<a;i++){
int x,y;
cin >> x >> y;
z[x].push_back(y);
z[y].push_back(x);
}
for (int i=1;i<=a;i++){
if (z[i].size()!=1){
root=i;
}
}
for (int i=1;i<=a;i++){
par[i]=i;
}
for (int i=1;i<=a;i++){
if (z[i].size()==1){
sz[i].push_back(i);
k++;
}
}
cout << (k+1)/2 << "\n";
dfs(root,0);
int x=find(root);
if (sz[x].size()%2==0){
for (int i=0;i<sz[x].size();i+=2){
cout << sz[x][i] << " " << sz[x][i+1] << "\n";
}
}else{
sz[x].push_back(root);
for (int i=0;i<sz[x].size();i+=2){
cout << sz[x][i] << " " << sz[x][i+1] << "\n";
}
}
return 0;
}
