#include <algorithm>
#include <bits/stdc++.h>
#include <cassert>
using namespace std;
#define ll long long
#define ff first
#define ss second
#define ln "\n"
const ll MOD = 998244353;
const ll INF = 2e18;
void solve(){
ll n; cin >> n;
vector<ll> deg(n);
for (ll i=0; i<n-1; i++){
ll u, v; cin >> u >> v; u--; v--;
deg[u]++; deg[v]++;
}
ll cnt=0; vector<ll> lf;
for (ll i=0; i<n; i++){
if (deg[i]==1) {lf.push_back(i); cnt++;}
}
cout << cnt%2+cnt/2 << ln;
for (ll i=1; i<(ll)lf.size(); i+=2){
cout << lf[i-1]+1 << " " << lf[i]+1 << ln;
}
if (lf.size()%2){
cout << lf[0]+1 << " " << lf.back()+1 << ln;
}
// ll n, m; cin >> n >> m;
// vector<vector<ll>> a(n, vector<ll>(m));
// for (ll i=0; i<n; i++){
// for (ll j=0; j<m; j++){
// char g; cin >> g;
// if (g=='R') a[i][j]=2;
// else if (g=='G') a[i][j]=1;
// }
// }
}
int main(){
ios_base::sync_with_stdio(0); cin.tie(nullptr);
ll t=1;
// cin >> t;
while (t--) solve();
}
