#include <bits/stdc++.h>
using namespace std;
vector <vector <int>> ad, gramezi;
vector <int> sub;
int nrf, cf;
void dfs(int nod, int par){
if(ad[nod].size() == 1)
sub[nod] = 1;
for(auto fiu : ad[nod])
if(fiu != par){
dfs(fiu, nod);
sub[nod] += sub[fiu];
}
}
int get_centroid(int nod, int par){
for(auto fiu : ad[nod])
if(fiu != par && sub[fiu] > nrf / 2)
return get_centroid(fiu, nod);
return nod;
}
bool cmp(const int &lhs, const int &rhs){
return gramezi[lhs].size() > gramezi[rhs].size();
}
void Frunza(int nod, int par, vector <int> &v){
if(ad[nod].size() == 1){
v.push_back(nod);
return;
}
for(auto fiu : ad[nod])
if(fiu != par)
Frunza(fiu, nod, v);
}
int main()
{
int n, x, y;
ios::sync_with_stdio(false);
cin >> n;
nrf = n;
ad.resize(n + 1);
sub.resize(n + 1);
for(int i = 1; i < n; i++){
cin >> x >> y;
ad[x].push_back(y);
ad[y].push_back(x);
}
dfs(1, 0);
nrf = sub[1];
cf = get_centroid(1, 0);
vector <int> pa;
for(auto fiu : ad[cf]){
vector <int> v;
pa.push_back(gramezi.size());
gramezi.push_back(v);
Frunza(fiu, cf, gramezi.back());
}
sort(pa.begin(), pa.end(), cmp);
cout << (nrf + 1) / 2 << '\n';
if(nrf % 2 == 1){
cout << cf << ' ' << gramezi[pa[0]].back() << '\n';
gramezi[pa[0]].pop_back();
sort(pa.begin(), pa.end(), cmp);
}
while(gramezi[pa[0]].size() > 0){
cout << gramezi[pa[0]].back() << ' ' << gramezi[pa[1]].back() << '\n';
gramezi[pa[0]].pop_back();
gramezi[pa[1]].pop_back();
sort(pa.begin(), pa.end(), cmp);
}
return 0;
}
