#include <bits/stdc++.h>
#define se second
#define fs first
#define mp make_pair
#define pb push_back
#define ll long long
#define ii pair<ll,ll>
#define ld long double
#define SZ(v) (int)v.size()
#define ALL(v) v.begin(), v.end()
#define bit(msk, i) ((msk >> i) & 1)
#define iter(id, v) for(auto id : v)
#define rep(i,m,n) for(int i=(m); i<=(n); i++)
#define reb(i,m,n) for(int i=(m); i>=(n); i--)
using namespace std;
mt19937_64 rd(chrono :: steady_clock :: now().time_since_epoch().count());
ll Rand(ll l, ll r) { return uniform_int_distribution<ll> (l, r)(rd); }
const int N = 5e5 + 7;
const int Mod = 998244353;
const int szBL = 916;
const ll INF = 1e18;
const int BASE = 137;
int n;
vector<int> ke[N];
int in[N], out[N];
vector<pair<int,int>> Ans;
vector<int> dfs (int u, int p) {
if (SZ(ke[u]) == 1) return vector<int> (1, u);
vector<int> prv;
iter (&v, ke[u]) {
if (v == p) continue;
vector<int> cur = dfs (v, u);
if (SZ(cur) > SZ(prv)) swap(cur, prv);
while (SZ(prv) + SZ(cur) > 2 && cur.size()) {
Ans.push_back(mp(cur.back(), prv.back()));
cur.pop_back();
prv.pop_back();
}
iter (&id, cur) prv.push_back(id);
}
return prv;
}
void solution () {
cin >> n;
rep (i, 1, n - 1) {
int u, v;
cin >> u >> v;
ke[u].push_back(v);
ke[v].push_back(u);
}
int root = 1;
rep (i, 1, n) if (SZ(ke[i]) > 1) root = i;
vector<int> cur = dfs (root, 0);
if (SZ(cur) == 1) cur.push_back(root);
Ans.push_back(mp(cur[0], cur[1]));
cout << SZ(Ans) <<"\n";
iter (&id, Ans) cout << id.fs<< " "<<id.se <<"\n";
}
#define file(name) freopen(name".inp", "r", stdin); freopen(name".out", "w", stdout);
int main () {
ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
// file ("fbuy");
int num_Test = 1;
// cin >> num_Test;
while (num_Test--)
solution();
}
/*
7
1 2 4
2 3 12
3 4 2
4 5 48
5 6 2
6 7 123
*/
