// IamHereForFun //
#include <bits/stdc++.h>
using namespace std;
#define LSOne(S) ((S) & -(S))
const int N = 5e5 + 5;
const int Q = 2e5 + 5;
const int M = 1e6 + 5;
const int LG = 18;
const int P = 31;
const long long INF = 4e18;
const int MOD = 1e9;
int n, sz = 0;
vector<vector<int>> adj(N);
vector<int> leaves;
void setLeaves(int cur, int par)
{
if (adj[cur].size() == 1)
{
leaves.push_back(cur);
}
for (int i : adj[cur])
{
if (i == par)
continue;
setLeaves(i, cur);
}
}
void prtSolve()
{
cin >> n;
for (int x = 0; x < n - 1; x++)
{
int a, b;
cin >> a >> b;
adj[a].push_back(b);
adj[b].push_back(a);
}
setLeaves(1, 0);
sz = leaves.size();
cout << (sz + 1) / 2 << "\n";
for (int x = 0; x < sz / 2; x++)
{
cout << leaves[x] << " " << leaves[x + (sz + 1) / 2] << "\n";
}
if (sz % 2 == 1)
{
cout << 1 << " " << leaves[sz / 2] << "\n";
}
}
signed main()
{
ios_base::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
int t = 1;
// cin >> t;
for (int x = 1; x <= t; x++)
{
prtSolve();
}
return 0;
}
