#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#include <bits/stdc++.h>
#define fi first
#define se second
#define pb push_back
#define sz(a) (int)a.size()
#define all(a) a.begin(), a.end()
#define rall(a) a.rbegin(), a.rend()
#define ff(i,a,b) for(int i=a;i<=b;i++)
#define fb(i,b,a) for(int i=b;i>=a;i--)
using namespace std;
using namespace __gnu_pbds;
typedef long long ll;
typedef pair<int,int> pii;
const int maxn = 500005;
const int inf = 1e9 + 5;
template<typename T>
using ordered_set = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
// os.order_of_key(k) the number of elements in the os less than k
// *os.find_by_order(k) print the k-th smallest number in os(0-based)
int n;
vector<int> g[maxn];
vector<int> leaf;
void dfs(int v, int p){
if(sz(g[v]) == 1)leaf.pb(v);
for(auto u : g[v]){
if(u != p)dfs(u, v);
}
}
int main()
{
ios::sync_with_stdio(false);
cout.tie(nullptr);
cin.tie(nullptr);
cin >> n;
ff(i,1,n - 1){
int u, v;
cin >> u >> v;
g[u].pb(v);
g[v].pb(u);
}
dfs(1, -1);
int len = (sz(leaf) + 1) / 2, add = sz(leaf) / 2;
cout << len << endl;
ff(i,0,len - 1)cout << leaf[i] << " " << leaf[i + add] << '\n';
return 0;
}
/**
8
4 1
8 2
1 3
5 7
4 8
6 1
4 7
// probati bojenje sahovski ili slicno
**/
