#include <bits/stdc++.h>
#define int long long int
#define ff first
#define ss second
#define FT ios_base::sync_with_stdio(false);cin.tie(0);
using namespace std;
const int maxn = 5e5 + 10;
int degree[maxn];
vector <int> leaf;
signed main()
{
FT;
int n;
cin >> n;
for (int i = 1 ; i < n ; i++)
{
int a , b;
cin >> a >> b;
degree[a]++;
degree[b]++;
}
for (int i = 1 ; i <= n ; i++)
{
if (degree[i] == 1)
{
leaf.push_back(i);
}
}
int k = leaf.size();
cout << (k + 1) / 2 << endl;
for (int i = 0 ; i < k - 1 ; i += 2)
{
cout << leaf[i] << " " << leaf[i + 1] << endl;
}
if (k % 2)
{
cout << leaf[k - 2] << " " << leaf[k - 1];
}
return 0;
}
