#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()
namespace CHECK_GRAPH {
vi tin, low, vis; int timer = 0;
bool pos = true;
int dfs(int u, int p, vvi &adj){
vis[u] = 1; tin[u] = low[u] = timer++;
bool so = false;
for(auto v : adj[u]){
if(v == p and !so) {so = true; continue;}
if(vis[v]) low[u] = min(low[u], tin[v]);
else low[u] = min(low[u], dfs(v, u, adj));
}
if(tin[u] == low[u] and u != p) pos = false;
return low[u];
}
void init(vvi &adj, int ROOT){
int N = adj.size();
tin.resize(N), low.resize(N);
vis.resize(N); dfs(ROOT, ROOT, adj);
}
};
vvi adj; vii bb;
vi solve(int u, int p){
if(adj[u].size() == 1) return {u};
vvi vec1, vec2;
for(auto v : adj[u]){
if(v == p) continue;
if(auto vec = solve(v, u); vec.size() == 1)
vec1.push_back(vec);
else vec2.push_back(vec);
}
vi vec;
auto ss = [&](vi nvec){
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));
};
for(auto vv : vec2) ss(vv);
for(auto vv : vec1) ss(vv);
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";
adj[u].push_back(v); adj[v].push_back(u);
}
CHECK_GRAPH::init(adj, ROOT);
assert(CHECK_GRAPH::pos);
return 0;
}
