#include <bits/stdc++.h>
#define int long long
using namespace std;
int a;
vector<int> z[1000005];
vector<int> v;
int sta[1000005];
int tour;
void dfs(int i, int parent) {
sta[i] = ++tour;
for (auto p : z[i]) {
if (p == parent) continue;
dfs(p, i);
}
}
bool cmp(int A, int B) {
return sta[A] < sta[B];
}
signed main() {
ios::sync_with_stdio(false);
cin.tie(NULL);
cin >> a;
for (int i = 1; i < a; i++) {
int x, y;
cin >> x >> y;
z[x].push_back(y);
z[y].push_back(x);
}
for (int i = 1; i <= a; i++) {
if (z[i].size() == 1) {
v.push_back(i);
}
}
dfs(1, 0);
int k = v.size();
cout << (k + 1) / 2 << "\n";
sort(v.begin(), v.end(), cmp);
if (k % 2 == 1) {
v.push_back(v[0]);
}
for (int i = 0; i < v.size(); i += 2) {
cout << v[i] << " " << v[i + 1] << "\n";
}
return 0;
}
