/* Man BINAHAYATO Mikham */
#include <bits/stdc++.h>
#define pb push_back
#define endl "\n"
#define ll long long
using namespace std;
const int maxn = 1e6 + 10, Maxn = 1e5 + 10, SQ = 360 , lg = 22 ;
const int mod = 1e9 + 7;
const long long inf = 1e18 + 10;
int sum[maxn], maxx[maxn], cnt, root;
vector<int> adj[maxn], vec;
void find_root(int v, int par){
for(auto u: adj[v]){
if(u == par)
continue;
find_root(u, v);
sum[v] += sum[u];
maxx[v] = max(maxx[v], sum[u]);
}
maxx[v] = max(maxx[v], cnt - sum[v]);
if(maxx[v] <= cnt/2)
root = v;
}
void dfs(int v, int par){
if(adj[v].size() == 1)
vec.pb(v);
for(auto u : adj[v])
if(par != u)
dfs(u, v);
}
int32_t main(){
ios:: sync_with_stdio(0), cin.tie(0), cout.tie(0);
int n;
cin >> n;
for(int i = 0 ; i < n - 1 ; i++){
int u, v;
cin >> u >> v;
u--, v--;
adj[u].pb(v);
adj[v].pb(u);
}
for(int i = 0 ; i < n ; i++)
if(adj[i].size() == 1)
cnt++;
find_root(0, -1);
dfs(root, -1);
int x = cnt/2;
cout << (cnt + 1)/2 << endl;
for(int i = 0 ; i < (cnt + 1)/2 ; i++){
cout << vec[i] + 1 << ' ' << vec[min(cnt - 1, i + x)] + 1 << endl;
}
return 0;
}
