// I stand with PALESTINE
// #pragma GCC optimize("Ofast,O3")
// #pragma GCC target("avx,avx2")
#include "bits/stdc++.h"
using namespace std;
using ll = long long;
void solve() {
int n;
cin >> n;
vector<vector<int>> g(n + 1);
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;
while (g[root].size() == 1) root++;
vector<int> vec;
auto dfs = [&](auto &dfs, int u, int p) -> void {
if (g[u].size() == 1) vec.emplace_back(u);
for (int v: g[u]) {
if (v != p) dfs(dfs, v, u);
}
};
dfs(dfs, root, -1);
cout << (vec.size() + 1) / 2 << '\n';
int l = 0, r = vec.size() - 1;
while (l < r) {
cout << vec[l] << ' ' << vec[r] << '\n';
l++, r--;
}
if (l <= r) cout << vec[0] << ' ' << vec[l] << '\n';
}
int main() {
cin.tie(0)->sync_with_stdio(false);
#ifdef sunnatov
freopen("input.txt", "r", stdin);
freopen("output.txt", "w", stdout);
#endif
int q = 1;
// cin >> q;
while (q--) {
solve();
// cout << '\n';
}
}
