#include<bits/stdc++.h>
using namespace std;
#define INIT ios_base :: sync_with_stdio(false); cin.tie(NULL); cout.tie(NULL);mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
#define mp make_pair
#define pb push_back
#define ft first
#define sc second
#define ll long long
#define pii pair<int, int>
#define count_bits __builtin_popcount
#define int ll
int t, n, m, k, a[300010], q, l, r;
int dg[500010];
int32_t main(){
INIT
cin>>n;
for(int i=1; i<n; i++){
int u, v;
cin>>u>>v;
dg[u]++; dg[v]++;
}
vector<int> v;
for(int i=1; i<=n; i++){
if(dg[i]==1){
v.pb(i);
}
}
vector<pii> res;
int lt=0;
while(v.size()>0){
if(v.size()==1){
res.pb({lt, v.back()});
v.pop_back();
}
else{
lt=v.back();
v.pop_back();
res.pb({lt, v.back()});
v.pop_back();
}
}
cout<<res.size()<<"\n";
for(auto pr:res){
cout<<pr.ft<<" "<<pr.sc<<"\n";
}
return 0;
}
