#include <bits/stdc++.h>
#define ll long long
#define ld long double
#define mp make_pair
#define pb push_back
#define in insert
#define vll vector<ll>
#define endl "\n"
#define pll pair<ll,ll>
#define all(x) (x).begin() , (x).end()
#define f first
#define s second
#define pr(x) cout<<x<<endl;
#define pr2(x,y) cout<<x<<" "<<y<<endl;
#define pr3(x,y,z) cout<<x<<" "<<y<<endl;
#define prv(v) for(auto x:v) cout<<x<<" ";
#define ffs fflush(stdout);
#define int ll
#define sz(x) (ll)x.size()
using namespace std;
const ll MOD = 1e9+7;
const ll INF = 1e9;
const ll LOG = 29;
#define PI 3.141592653589793238
long long binpow(long long a, long long b) {
a%=MOD;
long long res = 1;
while (b > 0) {
if (b & 1)
res = (res * a);
a = (a * a);
b >>= 1;
}
res%=MOD;
return res;
}
const ll N =(5e5+5);
vll adj[N];
vector<pll> ans;
ll dis[N];
void dfs(ll u,ll d,ll p){
dis[u] = d;
for(auto v:adj[u]){
if(v == p) continue;
dfs(v,d+1,u);
}
}
void solve(){
ll n;
cin>>n;
ll lf = 0;
for(int i = 2;i <= n;i++){
ll u,v;
cin >> u >> v;
adj[u].pb(v);
adj[v].pb(u);
}
for(int i =1;i <= n;i++){
if(sz(adj[i]) == 1){
lf++;
}
}
dfs(1,0,-1);
if(lf % 2 == 0){
cout << lf/2ll << endl;
vector<pll> gg;
for(int i = 1;i <= n;i++){
if(sz(adj[i]) == 1){
gg.pb(mp(dis[i],i));
}
}
sort(all(gg));
//ll xd = lf/2ll;
for(int i = 0;i+sz(gg)/2 < sz(gg);i++){
ans.pb(mp(gg[i].s,gg[i + sz(gg)/2].s));
}
for(auto x:ans){
cout<< x.f << ' '<< x.s <<endl;
}
return;
}
cout<<(lf+1)/2ll << endl;
vector<pll> gg;
for(int i = 1;i <= n;i++){
if(sz(adj[i]) == 1){
gg.pb(mp(dis[i],i));
}
}
sort(all(gg));
//ll xd = lf/2ll;
for(int i = 0;i+sz(gg)/2 < sz(gg);i++){
ans.pb(mp(gg[i].s,gg[i + sz(gg)/2].s));
}
// ll mid = sz(gg)/2;
// dfs(gg[mid].s,0,-1);
// ll ma = -1,nd =-1;
// for(int i =1;i<=n;i++){
// if(sz(adj[i]) == 1 && i != gg[mid].s && dis[i] > ma){
// ma = dis[i];
// nd =i ;
// }
// }
// ans.pb(mp(nd,gg[mid].s));
for(auto x:ans){
cout<< x.f << ' '<< x.s <<endl;
}
}
signed main(){
ios_base::sync_with_stdio(0);
cin.tie(NULL);
ll t=1;
//cin>>t;
while(t--){
solve();
}
}
