#include <bits/stdc++.h>
using namespace std;
#define cin(vec) for(auto& i : vec) cin >> i
#define cout(vec) for(auto& i : vec) cout << i << " "; cout << "\n";
#define fast ios::sync_with_stdio(0);cin.tie(0);
#define loop(i,a,b) for (int i = a; i < b; i++)
#define F first
#define S second
#define pb(n) push_back(n)
#define pf(n) push_front(n)
#define dci(d) fixed<<setprecision(d)
#define sp ' '
#define el '\n'
#define all(v) v.begin(),v.end()
#define int long long
int dx[8]= {0,0,1,-1,-1,1,1,-1};
int dy[8]= {-1,1,0,0,-1,1,-1,1};
int const N=5e5+5,M=1e3+1,Mod=1e9+7;
vector<int>adj[N],par[N];
vector<int>leaf;
int n;
void dfs(int u,int p){
if(adj[u].size()==1)leaf.push_back(u);
for(auto v:adj[u]){
if(v!=p)dfs(v,u);
}
}
void testcase(int h){
cin>>n;
for(int i=0;i<n-1;i++){
int u,v;cin>>u>>v;
adj[u].pb(v);
adj[v].pb(u);
}
dfs(1,-1);
// cout(leaf);
int sz=leaf.size();
if(sz%2){
cout<<sz/2+1<<el;
for(int i=0;i<sz/2;i++){
cout<<leaf[i]<<' '<<leaf[i+sz/2+1]<<el;
}
cout<<leaf[sz/2]<<' '<<1<<el;
}
else{
cout<<sz/2<<el;
for(int i=0;i<sz/2;i++){
cout<<leaf[i]<<' '<<leaf[i+sz/2]<<el;
}
}
}
int32_t main()
{
// fast
testcase(1);
// int tc;cin>>tc;for(int i=1;i<=tc;i++)testcase(i);
return 0;
}
