//package week4;
import java.io.*;
import java.util.*;
public class net {
public static void main(String[] args) throws IOException {
net obj = new net();
obj.doStuff();
}
int n;
ArrayList<Integer>[] graph;
int start;
int[] bit;
void upd(int n, int inc) {
n++;
while (n < bit.length) {
bit[n] += inc;
n += (n&-n);
}
}
int find(int n) {
int s = 0;
n++;
while (n > 0) {
s += bit[n];
n -= (n&-n);
}
return s;
}
int findfirst(int n) {
if (graph[n].size()==1) return etrev[n];
int l = 0, r = et.length, v = find(etrev[n]);
int best = et.length-1;
while (l < r) {
int m = (l+r)/2;
if (find(m) > v) {
best = m; r = m;
} else l = m+1;
}
return best;
}
int[] leaves;
int[] et; int count = 0;
int[] etrev;
int leaf(int n, int p) {
et[count] = n; count++;
etrev[et[count-1]] = count-1;
int vis = 0;
for (int i : graph[n]) {
if (i == p) continue;
vis += leaf(i, n);
}
if (vis == 0) {
leaves[n] = 1;
upd(count-1, 1);
return 1;
}
leaves[n] = vis;
return vis;
}
class SortArr implements Comparator<int[]> {
@Override
public int compare(int[] o1, int[] o2) {
return o2[1]-o1[1];
}
}
ArrayList<int[]> pairs = new ArrayList<>();
void process(int n, int p, int reps) {
int max = 0, pos = 0, sum = 0;
for (int i : graph[n]) {
if (i == p) continue;
sum += leaves[i];
if (leaves[i] > max) {
max = leaves[i];
pos = i;
}
}
int pairable = Math.min(sum, (sum-max)*2);
if (reps > pairable) {
process(pos, n, reps-pairable);
leaves[pos] = sum-max;
reps -= (reps-pairable);
}
PriorityQueue<int[]> pq = new PriorityQueue<>(new SortArr());
for (int i : graph[n]) {
if (i == p) continue;
pq.add(new int[] {i, leaves[i]});
}
while (reps > 1) {
int[] data1 = pq.poll();
int[] data2 = pq.poll();
int pos1 = findfirst(data1[0]);
int pos2 = findfirst(data2[0]);
upd(pos1, -1); upd(pos2, -1);
pairs.add(new int[] {et[pos1]+1, et[pos2]+1});
if (data1[1] > 1) pq.add(new int[] {data1[0], data1[1]-1});
if (data2[1] > 1) pq.add(new int[] {data2[0], data2[1]-1});
reps -= 2;
}
if (reps == 1) {
pairs.add(new int[] {et[pq.poll()[0]]+1, n+1});
}
}
@SuppressWarnings("unchecked")
private void doStuff() throws IOException {
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
n = Integer.parseInt(br.readLine());
graph = new ArrayList[n];
for (int i = 0; i < graph.length; i++) {
graph[i] = new ArrayList<>();
}
for (int i = 0; i < graph.length-1; i++) {
StringTokenizer st = new StringTokenizer(br.readLine());
int a = Integer.parseInt(st.nextToken())-1;
int b = Integer.parseInt(st.nextToken())-1;
graph[a].add(b);
graph[b].add(a);
}
br.close();
for (int i = 0; i < graph.length; i++) {
if (graph[i].size() > 1) {
start = i; break;
}
}
leaves = new int[graph.length];
et = new int[graph.length];
etrev = new int[graph.length];
bit = new int[graph.length+1];
leaf(start, -1);
process(start, -1, leaves[start]);
System.out.println(pairs.size());
for (int[] i : pairs) {
System.out.println(i[0]+" "+i[1]);
}
}
}
