import java.io.*;
import java.util.*;
public class net {
public static void main(String[] args) throws IOException{
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
int n = Integer.parseInt(br.readLine());
ArrayList<ArrayList<Integer>> graph = new ArrayList<>();
for(int i = 0; i < n; i++) graph.add(new ArrayList<Integer>());
for(int i = 1; i < n; i++) {
StringTokenizer st = new StringTokenizer(br.readLine());
int v1 = Integer.parseInt(st.nextToken()) - 1;
int v2 =Integer.parseInt(st.nextToken()) - 1;
graph.get(v1).add(v2);
graph.get(v2).add(v1);
}
int root = 0;
for(int i = 0; i < n; i++) {
if(graph.get(i).size() != 1) {
root = i;
}
}
int[] dist = new int[n];
Queue<Integer> q = new LinkedList<Integer>();
Arrays.fill(dist, -1);
q.add(root);
dist[root] = 0;
ArrayList<Integer> ans = new ArrayList<Integer>();
while(!q.isEmpty()) {
int node = q.poll();
for(int node2: graph.get(node)) {
if(dist[node2] == -1) {
dist[node2] = dist[node] + 1;
q.add(node2);
if(graph.get(node2).size() == 1) {
ans.add(node2 + 1);
}
}
}
}
PrintWriter pw = new PrintWriter(System.out);
pw.println((ans.size() + 1) / 2);
for(int i = 0; i < ans.size() / 2; i++) {
pw.println(ans.get(i) + " " + ans.get(i + ans.size() / 2));
}
if(ans.size() % 2 == 1) {
pw.println(ans.get(ans.size() - 1) + " " + ans.get(0));
}
pw.close();
}
}
