#include <algorithm>
#include <iostream>
#include <iomanip>
#include <numeric>
#include <cassert>
#include <vector>
#include <cmath>
#include <queue>
#include <set>
#include <map>
#define syosu(x) fixed<<setprecision(x)
using namespace std;
typedef long long ll;
typedef unsigned int uint;
typedef unsigned long long ull;
typedef pair<int,int> P;
typedef pair<double,double> pdd;
typedef pair<ll,ll> pll;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<double> vd;
typedef vector<vd> vvd;
typedef vector<ll> vl;
typedef vector<vl> vvl;
typedef vector<string> vs;
typedef vector<P> vp;
typedef vector<vp> vvp;
typedef vector<pll> vpll;
typedef pair<int,P> pip;
typedef vector<pip> vip;
const int inf=1<<29;
const ll INF=1ll<<60;
const double pi=acos(-1);
const double eps=1e-8;
const ll mod=998244353;
const int dx[4]={-1,0,1,0},dy[4]={0,-1,0,1};
int n;
vvi g;
vi a;
void dfs(int v,int p=0){
if(g[v].size()==1) a.push_back(v);
for(auto u:g[v]) if(u!=p) dfs(u,v);
}
int main(){
cin>>n;
g=vvi(n+1);
for(int i=1;i<n;i++){
int u,v;
cin>>u>>v;
g[u].push_back(v);
g[v].push_back(u);
}
dfs(1);
int m=a.size(),sz=(m+1)/2;
cout<<sz<<endl;
for(int i=0;i<sz;i++) cout<<a[i]<<' '<<a[i+m/2]<<endl;
}
