#include "bits/stdc++.h"
using namespace std;
void solve() {
int n;
cin >> n;
vector<vector<int>> g(n);
for (int i = 0, x, y; i + 1 < n; i++) {
cin >> x >> y;
x--, y--;
g[x].push_back(y);
g[y].push_back(x);
}
int rt = 0;
while ((int) g[rt].size() == 1) {
rt++;
}
vector<int> leafes;
auto dfs = [&] (auto&& dfs, int v, int pr) -> void {
if ((int) g[v].size() == 1) {
leafes.push_back(v);
}
for (auto u : g[v]) {
if (u != pr) {
dfs(dfs, u, v);
}
}
};
dfs(dfs, 0, 0);
int sz = (int) leafes.size();
vector<pair<int, int>> ans;
if (sz % 2 == 0) {
for (int i = 0; i < sz / 2; i++) {
ans.push_back({leafes[i], leafes[i + sz / 2]});
}
} else {
for (int i = 0; i < sz / 2; i++) {
ans.push_back({leafes[i], leafes[i + sz / 2]});
}
ans.push_back({leafes[0], leafes.back()});
}
cout << (int) ans.size() << '\n';
for (auto& [x, y] : ans) {
cout << x + 1 << " " << y + 1 << '\n';
}
}
int main() {
ios_base::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
int t = 1;
// cin >> t;
while (t--) {
solve();
}
}
