#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace std;
using namespace __gnu_pbds;
#define ordered_set tree<int, null_type,less<int>, rb_tree_tag,tree_order_statistics_node_update>
//#define int long long
#define pb push_back
#define pii pair<int,int>
#define F first
#define S second
const int maxn=5e5+7;
int n;
vector<int> adj[maxn];
void preprocess(){
cin>>n;
for(int i=1;i<n;i++){
int u,v;
cin>>u>>v;
adj[u].pb(v);
adj[v].pb(u);
}
}
vector<int> ans;
void dfs(int u,int p){
for(auto v : adj[u])
if(v != p)
dfs(v,u);
if(adj[u].size() == 1)
ans.pb(u);
}
void process(){
dfs(1,1);
}
void afterprocess(){
int javab=ans.size()/2;
cout<<javab+(ans.size()%2)<<'\n';
for(int i=0;i<javab;i++)
cout<<ans[i]<<' '<<ans[i+javab]<<'\n';
if(ans.size()%2)
cout<<ans[2*javab]<<' '<<ans[0]<<'\n';
}
int32_t main(){
ios_base::sync_with_stdio(0);
preprocess();process();afterprocess();
return 0;
}
