#include "bits/extc++.h"
using namespace std;
template <typename T, typename... U>
void dbgh(const T& t, const U&... u) {
cerr << t;
((cerr << " | " << u), ...);
cerr << endl;
}
#ifdef DEBUG
#define dbg(...) \
cerr << "L" << __LINE__ << " [" << #__VA_ARGS__ << "]" \
<< ": "; \
dbgh(__VA_ARGS__)
#else
#define cerr \
if (false) \
cerr
#define dbg(...)
#endif
#define endl "\n"
#define long int64_t
#define sz(x) int(std::size(x))
constexpr int maxn = 5e5 + 5;
int r1[maxn];
vector<pair<int, int>> ans;
vector<int> graph[maxn];
void pdfs(int u, int p, int r) {
if (r == -1 && p != -1) {
r = u;
}
r1[u] = r;
for (auto& v : graph[u]) {
if (v == p) {
continue;
}
pdfs(v, u, r);
}
}
vector<int> dfs(int u, int p) {
if (sz(graph[u]) == 1) {
return {u};
}
vector<int> unmatched;
for (auto& v : graph[u]) {
if (v == p) {
continue;
}
auto ch = dfs(v, u);
while (sz(unmatched) > 1 && sz(ch)) {
ans.emplace_back(unmatched.back(), ch.back());
unmatched.pop_back();
ch.pop_back();
}
unmatched.insert(unmatched.end(), begin(ch), end(ch));
assert(sz(unmatched) <= 3);
}
if (sz(unmatched) == 3) {
ans.emplace_back(unmatched[0], unmatched[1]);
unmatched = {unmatched[2]};
}
if (p == -1 && sz(unmatched)) {
if (sz(unmatched) == 2) {
ans.emplace_back(unmatched[0], unmatched[1]);
} else {
assert(sz(unmatched) == 1);
int left = unmatched[0];
for (auto& v : graph[u]) {
assert(v == r1[v]);
if (v != r1[left]) {
ans.emplace_back(v, left);
unmatched.pop_back();
break;
}
}
assert(!sz(unmatched));
}
}
return unmatched;
}
void solve() {
int n;
cin >> n;
for (int i = 0; i < n - 1; i++) {
int u, v;
cin >> u >> v;
u--;
v--;
graph[u].push_back(v);
graph[v].push_back(u);
}
for (int i = 0; i < n; i++) {
if (sz(graph[i]) < 2) {
continue;
}
pdfs(i, -1, -1);
dfs(i, -1);
break;
}
cout << sz(ans) << endl;
for (auto& [u, v] : ans) {
cout << u + 1 << " " << v + 1 << endl;
}
}
int main() {
cin.tie(nullptr);
cin.exceptions(ios::failbit);
ios_base::sync_with_stdio(false);
solve();
}
