#include <bits/stdc++.h>
using namespace std;
#define pii pair<int, int>
#define fi first
#define se second
const int maxn = 1e6 + 5;
int low[maxn], num[maxn], compid[maxn];
int timeDfs = 0, scc = 0;
vector<int> g[maxn];
set<int> adj[maxn];
stack<int> s;
void dfs2(int u, int pre){
low[u] = num[u] = ++timeDfs;
s.push(u);
for (int v: g[u]){
if (v != pre){
if (!num[v]){
dfs2(v, u);
low[u] = min(low[u], low[v]);
}
else low[u] = min(low[u], num[v]);
}
}
if (low[u] == num[u]){
while(true){
int v = s.top();
s.pop();
compid[v] = u;
if(v == u) break;
}
}
}
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);
}
dfs2(1, -1);
for(int u = 1; u <= n; u++){
for (int v: g[u]){
if (compid[u] != compid[v]){
adj[compid[u]].insert(compid[v]);
adj[compid[v]].insert(compid[u]);
}
}
}
int ans = 0;
vector<int> v;
for(int i = 1; i <= n; i++){
if(adj[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();
}
