#include <bits/stdc++.h>
using namespace std;
vector<vector<int>> adj;
vector<int> depth, low;
set<int> final;
vector<bool> visited;
int distanta = 0;
void dfs(int u, int parent) {
visited[u] = true;
depth[u] = low[u] = distanta++;
int children = 0;
for (int v : adj[u]) {
if (v == parent) continue;
if (!visited[v]) {
dfs(v, u);
low[u] = min(low[u], low[v]);
if ((parent == -1 && ++children > 1) || (parent != -1 && low[v] >= depth[u]))
final.insert(u);
} else {
low[u] = min(low[u], depth[v]);
}
}
}
int main() {
int n, a, b;
cin >> n;
adj.resize(n + 1);
depth.resize(n + 1);
low.resize(n + 1);
visited.assign(n + 1, false);
for (int i = 0; i < n; ++i) {
cin >> a >> b;
adj[a].push_back(b);
adj[b].push_back(a);
}
dfs(1, -1);
vector<int> deg(n + 1, 0);
for (int i = 1; i <= n; ++i) {
if (final.count(i)) {
for (int v : adj[i])
if (!final.count(v))
deg[v]++;
}
}
vector<int> leaves;
for (int i = 1; i <= n; ++i)
if (!final.count(i) && deg[i] == 1)
leaves.push_back(i);
cout << (leaves.size() + 1) / 2 << "\n";
for (int i = 0; i + 1 < leaves.size(); i += 2)
cout << leaves[i] << " " << leaves[i + 1] << "\n";
if (leaves.size() % 2 == 1) {
int leaf = leaves.back();
int fallback = *final.begin();
cout << leaf << " " << fallback << "\n";
}
}
