// Restart
// += O(logn) ; + = O(n)
//#pragma GCC optimize("Ofast")
//#pragma GCC optimize("unroll-loops")
//#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")
#include<bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp> // Common file
#include <ext/pb_ds/tree_policy.hpp> // Including tree_order_statistics_node_update
#define fastio ios_base::sync_with_stdio(0);cin.tie(0)
#define fst first
#define snd second
#define all(x) (x).begin(), (x).end()
#define pb push_back
#define sz size()
#define FORN(i,j,n) for(int i=j; i<(int)n;i++)
#define FOR(i,n) FORN(i,0,n)
#define FORIT(i,x) for( auto i = x.begin() ; i != x.end() ; i++ )
#define MOD 998244353LL
#define MOD1 1000000007LL
#define LIM 262150
#define ones(x) __builtin_popcount(x)
#define trace(x) cerr << #x << ": " << x << endl;
#define trace2(x, y) cerr << #x << ": " << x << " | " << #y << ": " << y << endl;
#define trace3(x, y,z) cerr << #x << ": " << x << " | " << #y << ": " << y << " | " << #z << ": " << z << endl;
#define INF 1000000000
#define in(x) cin>>x;
#define out(x) cout<<x;
#define MAXIMO 1LL<<60
#define loga2(x) __builtin_ctzll(x)
//SOLO PARA POTENCIAS DE 2
using namespace std;
using namespace __gnu_pbds;
typedef long long ll ;
typedef unsigned long long ull ;
typedef vector <int> vi;
typedef pair <int,int> ii;
typedef pair <int,ii> iii;
typedef vector <string> vs;
typedef vector <ii> vii;
typedef vector <iii> viii;
typedef tree<int,null_type,less<int>,rb_tree_tag,tree_order_statistics_node_update> ordered_set;
vi G[500005];
vi ans;
void dfs(int curr, int ant = -1){
bool leaf = true;
for(auto v: G[curr]) {
if(ant != v){
dfs(v,curr);
leaf=false;
}
}
if(leaf) ans.pb(curr);
}
void go(){
int n; cin>>n;
for(int i=1; i<n;i++){
int x, y; cin >> x >> y;
G[x].pb(y);
G[y].pb(x);
}
//Input is a tree
for(int i=1; i<=n; i++){
if(G[i].size() != 1){
dfs(i);
break;
}
}
cout<< (ans.size() + 1)/2 <<"\n";
for(int i=0; i< (ans.size()+1)/2; i++){
cout<<ans[i] << " " << ans[i + ans.size()/2 ]<<"\n";
}
}
void timer(){
clock_t begin = clock();
go();
clock_t end = clock();
double time_spent = (double)(end - begin) / CLOCKS_PER_SEC;
cout<<time_spent<<"\n";
}
int main() {
//fastio;
go();
//timer();
return 0;
}
