#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
typedef long double ld;
typedef vector<int> vi;
typedef pair<int, int> ii;
typedef vector<ii> vii;
typedef vector<vi> vvi;
typedef vector<vii> vvii;
#define INF INT_MAX
#define MOD 1000000007
#define all(x) x.begin(), x.end()
vvi adj; vii bb;
vi solve(int u, int p){
if(adj[u].size() == 1) return {u};
vi vec;
for(auto v : adj[u]){
if(v == p) continue;
vi nvec = solve(v, u);
while(vec.size() and nvec.size() and vec.size()+nvec.size() > 2-(u==p)){
bb.push_back({vec.back(), nvec.back()});
vec.pop_back(); nvec.pop_back();
}
vec.insert(vec.end(), all(nvec));
}
if(u == p and vec.size()){
bb.push_back({vec.back(), u});
}
return vec;
}
int main(){
ios::sync_with_stdio(false);
cin.tie(NULL);
int N; cin >> N;
adj.resize(N);
for(int x = 0; x < N-1; x++){
int u, v; cin >> u >> v;
u--, v--;
adj[u].push_back(v);
adj[v].push_back(u);
}
int ROOT = 0;
for(int x = 0; x < N; x++)
if(adj[x].size() > 1) ROOT = x;
solve(ROOT, ROOT);
cout << bb.size() << endl;
for(auto [u, v] : bb)
cout << u+1 << " " << v+1 << "\n";
return 0;
}
