#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef pair<int, int> pii;
const int MAX = 2e6 + 15;
const int INF = 0x3f3f3f3f;
const int MOD = 1e9 + 7;
#define pb push_back
#define sz(x) (int) x.size()
#define fr first
#define sc second
#define mp make_pair
#define all(x) x.begin(), x.end()
#define dbg(x) cout << #x << ": " << "[ " << x << " ]\n"
int n;
vector<int> adj[MAX], l;
void setIO(){
ios_base::sync_with_stdio(false);
cin.tie(NULL);
}
void dfs(int x, int p){
if(sz(adj[x]) == 1){
l.pb(x);
}
for(auto v : adj[x]){
if(v == p) continue;
dfs(v, x);
}
}
int main(){
setIO();
cin >> n;
for(int i = 1; i < n; i++){
int u, v; cin >> u >> v;
adj[u].pb(v);
adj[v].pb(u);
}
dfs(1, -1);
int e = sz(l) / 2 + (sz(l) % 2);
cout << e << '\n';
for(int i = 0; i < e; i++){
int u = l[i], v = (i + sz(l)/2 < sz(l) ? l[i + sz(l)/2] : l[0]);
cout << u << ' ' << v << '\n';
}
return 0;
}
