#include <bits/stdc++.h>
using namespace std;;
#define ll long long
#define ar array
#define ld long double
#define int long long
#define all(v) v.begin(), v.end()
const int N = 1e6 + 20;
const int K = 469;
const int LOG = 26;
const int INF = 1e12;
int MOD = 998244353;
vector<int> g[N];
vector<int> ord;
void dfs(int x, int p){
if(g[x].size() == 1)ord.push_back(x);
for(auto u: g[x]){
if(u == p)continue;
dfs(u, x);
}
}
void orz(){
int n;
cin>>n;
for(int i = 1;i < n;i++){
int a, b;
cin>>a>>b;
--a, --b;
g[a].push_back(b);
g[b].push_back(a);
}
dfs(0, 0);
int cnt = ord.size();
cout<<(cnt + 1) / 2<<'\n';
for(int i = 0;i < cnt / 2;i++)cout<<ord[i] + 1<<" "<<ord[i + cnt / 2] + 1<<'\n';
if(cnt % 2)cout<<ord[0] + 1<<" "<<ord[cnt - 1] + 1;
}
signed main(){ios_base::sync_with_stdio(false);cin.tie(0);
int t;
//cin>>t;
t = 1;
while(t--)orz();
}
