#include <bits/stdc++.h>
using namespace std;
#define int long long
#define ld long double
#define show(x,y) cout << y << " " << #x << endl;
#define show2(x,y,i,j) cout << y << " " << #x << " " << j << " " << #i << endl;
#define show3(x,y,i,j,p,q) cout << y << " " << #x << " " << j << " " << #i << " " << q << " " << #p << endl;
#define show4(x,y) for(auto it:x) cout << it << " "; cout << #y << endl;
typedef pair<long long,long long>pii;
typedef pair<pii,pii>pi2;
vector<int>adj[500005];
vector<int>leaf;
void dfs(int index, int par){
if(adj[index].size()==1)leaf.push_back(index);
for(auto it:adj[index]){
if(it==par) continue;
dfs(it,index);
}
}
void solve(){
int n;
cin >> n;
int temp,temp2;
for(int x=0;x<n-1;x++){
cin >> temp >> temp2;
adj[temp].push_back(temp2);
adj[temp2].push_back(temp);
}
for(int x=1;x<=n;x++){
if(adj[x].size()>1){
dfs(x,-1);
break;
}
}
int sz=leaf.size();
cout << (sz+1)/2 << "\n";
for(int x=sz/2;x<sz;x++){
cout << leaf[x] << " " << leaf[x-sz/2] << "\n";
}
cout << "\n";
}
int32_t main(){
ios::sync_with_stdio(0);
cin.tie(0);
int t=1;
//cin >> t;
while(t--){
solve();
}
}
