#include "bits/stdc++.h"
using namespace std;
#ifdef duc_debug
#include "bits/debug.h"
#else
#define debug(...)
#endif
const int maxn = 5e5 + 5;
int n, h[maxn];
vector<int> g[maxn];
vector<int> leaves;
void pre_dfs(int u, int prev) {
if ((int)g[u].size() == 1) {
leaves.push_back(u);
}
for (auto v:g[u]) {
if (v == prev) continue;
h[v] = h[u] + 1;
pre_dfs(v, u);
}
}
void solve() {
cin >> n;
int root = 0;
for (int i = 1; i < n; ++i) {
int u, v; cin >> u >> v;
g[u].push_back(v);
g[v].push_back(u);
}
for (int i = 1; i <= n; ++i) {
if ((int)g[i].size() > 1) {
root = i;
break;
}
}
pre_dfs(root, 0);
cout << ((int)leaves.size() + 1) / 2 << '\n';
for (int i = 0; i < ((int)leaves.size() + 1) / 2; ++i) {
if (i == (int)leaves.size() / 2) {
cout << leaves[i] << " " << leaves[0] << '\n';
} else {
cout << leaves[i] << " " << leaves[i + (int)leaves.size() / 2] << '\n';
}
}
}
signed main() {
ios_base::sync_with_stdio(0);
cin.tie(0);
solve();
return 0;
}
