#include <bits/stdc++.h>
using ll = long long;
using std::vector;
using std::array;
using std::pair;
using std::tuple;
template <class T> constexpr T infty = std::numeric_limits<T>::max() / 2;
template <class F> struct rec_lambda : private F {
explicit rec_lambda(F&& f) : F(std::forward<F>(f)) {}
template <class... Args> decltype(auto) operator()(Args&&... args) const {
return F::operator()(*this, std::forward<Args>(args)...);
}
};
int main() {
std::ios_base::sync_with_stdio(false);
std::cin.tie(nullptr);
int N;
std::cin >> N;
vector<vector<int>> graph(N);
for (int i = 0; i < N - 1; ++i) {
int a, b;
std::cin >> a >> b;
a -= 1, b -= 1;
graph[a].push_back(b);
graph[b].push_back(a);
}
vector<int> size(N);
rec_lambda([&](auto&& dfs, const int u, const int p) -> void {
size[u] = (int)graph[u].size();
for (const int v : graph[u]) {
if (v != p) {
dfs(v, u);
size[u] += size[v];
}
}
})(0, -1);
const int L = size[0];
const int centroid = [&] {
int u = 0, p = -1;
while (true) {
bool found = false;
for (const int v : graph[u]) {
if (v != p and size[v] > L / 2) {
p = u;
u = v;
found = true;
break;
}
}
if (!found) {
break;
}
}
return u;
}();
vector<int> list;
for (const int root : graph[centroid]) {
rec_lambda([&](auto&& dfs, const int u, const int p) -> void {
if (graph[u].size() == 1) {
list.push_back(u);
}
for (const int v : graph[u]) {
if (v != p) {
dfs(v, u);
}
}
})(root, centroid);
}
if (list.size() % 2 == 1) {
list.push_back(0);
}
const int H = list.size() / 2;
std::cout << H << '\n';
for (int i = 0; i < H; ++i) {
std::cout << list[i] + 1 << ' ' << list[i + H] + 1 << '\n';
}
return 0;
}
