#include <bits/stdc++.h>
#define int long long
using namespace std;
namespace std {
template <typename T> ostream &operator<<(ostream &out, const vector<T> &vec) {
out << "[";
for (int i = 0; i < (int)vec.size(); ++i) {
out << vec[i];
if (i + 1 < (int)vec.size())
out << ", ";
}
return out << "]";
}
} // namespace std
void dbg_out() { cout << endl; }
template <typename Head, typename... Tail> void dbg_out(Head H, Tail... T) {
cout << ' ' << H;
dbg_out(T...);
}
#ifdef DEBUG
#define dbg(...) cout << "(" << #__VA_ARGS__ << "):", dbg_out(__VA_ARGS__)
#else
#define dbg(...)
#endif
signed main(void) {
ios_base::sync_with_stdio(false);
cin.tie(0);
int nbSommet;
cin >> nbSommet;
vector<vector<int>> adj(nbSommet);
for (int i = 1; i < nbSommet; ++i) {
int u, v;
cin >> u >> v;
--u, --v;
adj[u].push_back(v);
adj[v].push_back(u);
}
vector<int> feuilles;
auto DFS = [&](auto dfs, int u, int p) -> void {
if (adj[u].size() == 1)
feuilles.push_back(u);
for (int v : adj[u])
if (v != p)
dfs(dfs, v, u);
};
for (int u = 0; u < nbSommet; ++u)
if (adj[u].size() > 1) {
DFS(DFS, u, u);
break;
}
int nbFeuilles = feuilles.size();
int delta = (nbFeuilles + 1) / 2;
cout << (nbFeuilles + 1) / 2 << endl;
for (int i = 0; i < (nbFeuilles + 1) / 2; ++i)
cout << 1 + feuilles[i] << ' ' << feuilles[(i + delta) % nbFeuilles] + 1
<< '\n';
}
