#include <bits/stdc++.h>
using namespace std;
vector<int> a;
void f (int p, int n, vector<vector<int>> & g) {
if ((int)g[n].size() == 1) a.push_back(n);
for (int c: g[n]) {
if (c != p) f (n, c, g);
}
}
int main() {
ios::sync_with_stdio(false);
cin.tie(NULL); cout.tie(NULL);
int n, u, v, s;
cin >> n;
vector<vector<int>> g(n, vector<int>());
for (int i = 0; i < n-1; i++) {
cin >> u >> v;
u--; v--;
g[u].push_back(v);
g[v].push_back(u);
}
f (-1, 0, g);
cout << ((int)a.size() + 1) / 2 << '\n';
s = (int)a.size() / 2;
for (int i = 0; i < s; i++) {
cout << a[i] + 1 << ' ' << a[s+i] + 1 << '\n';
}
s = (int)a.size();
if (s % 2 == 1) cout << a[0] + 1 << ' ' << a[s-1] + 1 << '\n';
return 0;
}
