/*
Code by @marlov
*/
#include <iostream>
#include <fstream>
#include <string>
#include <sstream>
#include <vector>
#include <string>
#include <cmath>
#include <algorithm>
#include <iomanip>
#include <utility>
#include <set>
#include <unordered_set>
#include <map>
#include <unordered_map>
#include <stack>
#include <queue>
#include <iterator>
using namespace std;
typedef long long ll;
typedef pair<int,int> pi;
#define maxN 500005
int N;
int tl=0;
int leaves[maxN];
int root=0;
vector<int> adj[maxN];
vector< pair<int,int> > edges;
vector< vector<int> > connect;
priority_queue< pair<int,int> > pq;
void findRoot(int n,int p){
if(adj[n].size()==1){
leaves[n]++;
}
bool wks=true;
for(int i:adj[n]) if(i!=p){
findRoot(i,n);
if(leaves[i]>floor(tl/2)) wks=false;
leaves[n]+=leaves[i];
}
if(tl-leaves[n]>floor(tl/2)) wks=false;
if(wks&&adj[n].size()>1) root=n;
}
void addL(int n,int p){
if(adj[n].size()==1){
connect.back().push_back(n);
return;
}
for(int i:adj[n]) if(i!=p){
addL(i,n);
}
}
int main() {
ios_base::sync_with_stdio(0); cin.tie(0);
cin>>N;
int u,v;
for(int i=0;i<N-1;i++){
cin>>u>>v;
u--;v--;
adj[u].push_back(v);
adj[v].push_back(u);
}
for(int i=0;i<N;i++){
if(adj[i].size()==1) tl++;
}
findRoot(0,-1);
for(int i:adj[root]){
int ci=connect.size();
connect.push_back(vector<int>(0));
addL(i,root);
pq.push(make_pair(connect[ci].size()-1,ci));
}
while(pq.size()>1){
int fi=pq.top().second;
int fl=pq.top().first; pq.pop();
int sl=pq.top().first;
int si=pq.top().second;pq.pop();
edges.push_back(make_pair(connect[fi][fl],connect[si][sl]));
if(fl>0) pq.push(make_pair(fl-1,fi));
if(sl>0) pq.push(make_pair(sl-1,si));
}
if(pq.size()==1){
edges.push_back(make_pair(connect[pq.top().second].front(),root));
}
cout<<edges.size()<<'\n';
for(int i=0;i<(int)edges.size();i++){
cout<<edges[i].first+1<<" "<<edges[i].second+1<<'\n';
}
return 0;
}
/* stuff you should look for
* int overflow, array bounds
* special cases (n=1,n=0?)
* do smth instead of nothing and stay organized
*/
