#include <bits/stdc++.h>
using namespace std;
const int kN = 5e5;
vector<int> g[1 + kN], a;
void dfs(int u, int par) {
if ((int)g[u].size() == 1) {
a.emplace_back(u);
}
for (int v : g[u]) {
if (v != par) {
dfs(v, u);
}
}
}
/*
9
1 2
2 3
2 4
2 5
1 6
1 7
3 8
3 9
*/
void testCase() {
int n;
cin >> n;
for (int i = 1; i < n; ++i) {
int u, v;
cin >> u >> v;
g[u].emplace_back(v);
g[v].emplace_back(u);
}
int root = -1;
for (int v = 1; v <= n; ++v) {
if ((int)g[v].size() > 1) {
root = v;
}
}
dfs(root, 0);
cout << (a.size() + 1) / 2 << '\n';
for (int i = 0, j = a.size() - 1; i < j; ++i, --j) {
cout << a[i] << ' ' << a[j] << '\n';
}
if ((int)a.size() % 2 == 1) {
cout << root << ' ' << a[a.size() / 2] << '\n';
}
}
int main() {
ios_base::sync_with_stdio(false);
cin.tie(nullptr);
int tests = 1;
for (int tc = 0; tc < tests; ++tc) {
testCase();
}
return 0;
}
