#include <bits/stdc++.h>
using namespace std;
int main()
{
ios::sync_with_stdio(0);
cin.tie(nullptr);
int n, t1, t2;
cin >> n;
vector<int> net(n + 1, 0);
vector<vector<int>> conwith(n + 1);
vector<int> con;
for (int i = 1; i < n; i++)
{
cin >> t1 >> t2;
net[t1]++;
net[t2]++;
conwith[t1].emplace_back(t2);
conwith[t2].emplace_back(t1);
}
int c = 0;
for (int i = 1; i <= n; i++)
{
if (net[i] == 1)
con.push_back(i);
}
int center = 1;
for (int i = 1; i <= n; i++)
{
if (net[i] > 1)
{
center = i;
break;
}
}
int leafCount = con.size();
int pairs = (leafCount + 1) / 2;
cout << pairs << "\n";
int l = 0, r = leafCount - 1;
while (l < r)
{
cout << con[l] << " " << con[r] << "\n";
l++;
r--;
}
if (l == r)
{
cout << con[l] << " " << center << "\n";
}
}
