#include <bits/stdc++.h>
#include <cstdio>
#include <cstring>
#include <cmath>
#include <cstring>
#include <chrono>
#include <complex>
#define endl "\n"
#define ll long long int
#define vi vector<int>
#define vll vector<ll>
#define vvi vector < vi >
#define pii pair<int,int>
#define pll pair<long long, long long>
#define mod 1000000007
#define inf 1000000000000000001;
#define all(c) c.begin(),c.end()
#define mp(x,y) make_pair(x,y)
#define mem(a,val) memset(a,val,sizeof(a))
#define pb push_back
#define f first
#define s second
#define pi 3.141592653589793238
using namespace std;
ll gcd( ll a, ll b )
{
if(b==0)
{
return a;
}
else
{
return gcd( b, a%b );
}
}
ll lcm (ll a, ll b)
{
return (a*b)/gcd(a,b);
}
ll power(ll a, ll b) //a is base, b is exponent
{
if(b==0)
return 1;
if(b==1)
return a;
if(b%2 == 1)
return (power(a,b-1)*a)%mod;
ll q = power(a,b/2);
return (q*q)%mod;
}
vector<int> adj[500005];
vector<int> leaf;
void dfs(int u,int p){
for(auto v:adj[u]){
if(v!=p){
dfs(v,u);
}
}
if(adj[u].size() == 1)
leaf.pb(u);
}
int main()
{
std::ios::sync_with_stdio(false);
int n;
cin >> n;
for(int i =2;i<=n;i++){
int u,v;
cin >> u >> v;adj[u].pb(v);adj[v].pb(u);
}
dfs(1,-1);
reverse(leaf.begin(),leaf.end());
// for(auto &x:leaf) cout << x << " ";cout<<endl;
if(leaf.size() & 1){
cout << ((leaf.size() + 1) >> 1) << endl;
for(int i = 0,j=leaf.size()-1;i<j;i++,j--){
cout << leaf[i] << " " << leaf[j] << endl;
}
cout << leaf[0] << " " << leaf[leaf.size()/2] << endl;
}
else{
cout << ((leaf.size() + 1) >> 1) << endl;
for(int i = 0,j=leaf.size()-1;i<j;i++,j--){
cout << leaf[i] << " " << leaf[j] << endl;
}
}
return 0;
}
//Hello, this is a snippet.
