// Judges with GCC >= 12 only needs Ofast
// #pragma GCC optimize("O3,no-stack-protector,fast-math,unroll-loops,tree-vectorize")
// MLE optimization
// #pragma GCC optimize("conserve-stack")
// Old judges
// #pragma GCC target("sse4.2,popcnt,lzcnt,abm,mmx,fma,bmi,bmi2")
// New judges. Test with assert(__builtin_cpu_supports("avx2"));
// #pragma GCC target("avx2,popcnt,lzcnt,abm,bmi,bmi2,fma,tune=native")
// Atcoder
// #pragma GCC target("avx2,popcnt,lzcnt,abm,bmi,bmi2,fma")
/*
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace __gnu_pbds;
typedef tree<int,null_type,less<int>,rb_tree_tag,tree_order_statistics_node_update> ordered_set;
- insert(x),erase(x)
- find_by_order(k): return iterator to the k-th smallest element
- order_of_key(x): the number of elements that are strictly smaller
*/
#include<bits/stdc++.h>
using namespace std;
mt19937_64 rng(chrono::steady_clock::now().time_since_epoch().count());
uniform_real_distribution<> pp(0.0,1.0);
//#define int long long
#define ld long double
#define pii pair<int,int>
#define piii pair<int,pii>
#define mpp make_pair
#define fi first
#define se second
//const int inf=1e18;
const int mod=998244353;
const int maxn=500005;
const int bl=650;
const int maxs=655;
const int maxm=200005;
const int maxq=1000005;
const int maxl=20;
const int maxa=1000000;
const int root=3;
/*
int power(int a,int n){
int res=1;
while(n){
if(n&1) res=res*a%mod;
a=a*a%mod;n>>=1;
}
return res;
}
const int iroot=power(3,mod-2);
*/
const int base=101;
pii p[maxn];
vector<pii> ans;
vector<int> edge[maxn];
void dfs(int u,int par){
if((int)edge[u].size()==1){
p[u]={-1,u};
return;
}
deque<int> f1;
pii f2={-1,-1};
for(int v:edge[u]){
if(v==par) continue;
dfs(v,u);
if(p[v].fi==-1) f1.push_back(p[v].se);
else if(f2.fi==-1) f2=p[v];
else{
ans.push_back({f2.se,p[v].fi});
f2.se=p[v].se;
}
}
if(f2.fi!=-1){
f1.push_front(f2.fi);
f1.push_back(f2.se);
}
while((int)f1.size()>=3){
int x=f1.back();f1.pop_back();
int y=f1.back();f1.pop_back();
ans.push_back({x,y});
}
if((int)f1.size()>=2) p[u]={f1[0],f1[1]};
else p[u]={-1,f1[0]};
}
void solve(){
int n;cin >> n;
for(int i=1;i<n;i++){
int u,v;cin >> u >> v;
edge[u].push_back(v);
edge[v].push_back(u);
}
int rt=1;
while((int)edge[rt].size()==1) rt++;
dfs(rt,0);
if(p[rt].fi==-1) ans.push_back({rt,p[rt].se});
else ans.push_back(p[rt]);
cout << (int)ans.size() << '\n';
for(auto &[x,y]:ans) cout << x << ' ' << y << '\n';
}
signed main(){
ios_base::sync_with_stdio(false);
cin.tie(NULL);cout.tie(NULL);
int test=1;//cin >> test;
while(test--) solve();
}
