#include <bits/stdc++.h>
using namespace std;
#define pb push_back
#define fi first
#define se second
#define TranLeThanhTam "TranLeThanhTam"
#define all(v) v.begin(),v.end()
#define reset(a,i) memset(a,i,sizeof(a))
#define FOR(i,a,b) for (int i = (a), _b = (b); i <= _b; ++i)
#define FORD(i,a,b) for (int i = (a), _b = (b); i >= _b; --i)
#define compact(v) sort(all(v)), v.erase(unique(all(v)), end(v))
#define sz(v) (int) v.size()
#define MASK(i) (1 << (i))
typedef long long ll;
typedef long double lb;
typedef pair<ll,ll> pll;
typedef pair<int,int> pii;
const int Thanh_Tam = 5 * 1e5 + 17;
const int inf = 1e9 + 17;
const long long infll = 1e18 + 17;
const int MOD = 1e9 + 7;
const int Log = 17;
const int dx[4] = {-1, 0, 0, 1};
const int dy[4] = {0, -1, 1, 0};
const int max_block_size = 270;
const ll P = 311;
const int maxA = 1e2 + 17;
const int addi = 1e9;
const char dir[4] = {'W', 'S', 'N', 'E'};
const int Mod[3] = {998244353, MOD, 759186269};
ll mul(ll a, ll b, ll mod);
ll binpow(ll a, ll b, ll mod)
{
ll res = 1;
while (b > 0)
{
if (b & 1) res = mul(res,a,mod);
b >>= 1;
a = mul(a,a,mod);
}
return res;
}
ll add(ll a, ll b, ll mod) { return (a + b) % mod; }
ll sub(ll a, ll b, ll mod) { return (a - b + mod) % mod; }
ll mul(ll a, ll b, ll mod) { return ((a % mod) * (b % mod)) % mod; }
ll div(ll a, ll b, ll mod) { return mul(a, binpow(b, mod - 2, mod), mod); }
mt19937 rng(chrono::high_resolution_clock::now().time_since_epoch().count());
ll rand_range(ll l, ll r){return uniform_int_distribution<ll>(l, r)(rng);}
int n, root = 1;
vector<int> adj[Thanh_Tam];
deque<int> leaf[Thanh_Tam];
vector<pii> need_edges;
void dp_on_tree(int u, int par = 0)
{
if (sz(adj[u]) == 1)
{
leaf[u].pb(u);
return;
}
for (int v : adj[u])
{
if (par == v) continue;
dp_on_tree(v, u);
if (sz(leaf[v]) > 0)
for (int k : leaf[v]) leaf[u].pb(k);
leaf[v].clear();
if (sz(leaf[u]) > 2)
{
int x = leaf[u].back();
leaf[u].pop_back();
int y = leaf[u].front();
leaf[u].pop_front();
need_edges.pb({x, y});
}
}
return;
}
signed main()
{
ios_base::sync_with_stdio(false);
cin.tie(NULL);
cout.tie(NULL);
if (fopen(TranLeThanhTam".inp","r"))
{
freopen(TranLeThanhTam".inp","r",stdin);
freopen(TranLeThanhTam".out","w",stdout);
}
cin >> n;
FOR(i,2,n)
{
int u,v;
cin >> u >> v;
adj[u].pb(v);
adj[v].pb(u);
}
FOR(i,1,n)
if (sz(adj[i]) > 1)
{
root = i;
break;
}
dp_on_tree(root);
if (sz(leaf[root]) > 0)
{
if (sz(leaf[root]) == 2) need_edges.pb({leaf[root][0], leaf[root][1]});
else need_edges.pb({need_edges.back().se, leaf[root].back()});
}
cout << sz(need_edges) << '\n';
for (pii k : need_edges) cout << k.fi << ' ' << k.se << '\n';
return 0;
}
