#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
const int N = 5e5 + 7;
vector <int> g[N];
vector <int> l;
int tin[N];
int timer;
void dfs(int v, int pr) {
tin[v] = timer++;
if (g[v].size() == 1) {
l.push_back(v);
}
for (int to : g[v]) {
if (to != pr) {
dfs(to, v);
}
}
}
int main() {
ios::sync_with_stdio(0);
cin.tie(0);
int n;
cin >> n;
for (int i = 0; i < n - 1; i++) {
int a, b;
cin >> a >> b;
a--, b--;
g[a].push_back(b);
g[b].push_back(a);
}
dfs(0, -1);
sort(l.begin(), l.end(), [&] (int a, int b) {
return tin[a] < tin[b];
});
int k = (int) l.size();
int m = k / 2;
cout << (k + 1) / 2 << '\n';
for (int i = 0; i < (k + 1) / 2; i++) {
cout << l[i] + 1 << ' ' << l[(i + m) % k] + 1 << '\n';
}
return 0;
}
