#include <bits/stdc++.h>
using namespace std;
#define pii pair<int, int>
#define fi first
#define se second
const int maxn = 1e6 + 5;
vector<int> g[maxn];
void solve (){
int n; cin >> n;
for(int i = 1; i <= n - 1; i++){
int u, v; cin >> u >> v;
g[u].push_back(v);
g[v].push_back(u);
}
int ans = 0;
vector<int> v;
for(int i = 1; i <= n; i++){
if(g[i].size() == 1){
ans++;
v.push_back(i);
}
}
cout << (ans + 1) / 2 << "\n";
if(v.size() % 2 == 1) cout << 1 << " " << v.back() << "\n";
for(int i = 0; i + 1 < v.size(); i += 2){
cout << v[i] << " " << v[i + 1] << "\n";
}
}
signed main() {
ios_base::sync_with_stdio(false);
cin.tie(0); cout.tie(0);
solve();
}
