# include <bits/stdc++.h>
/*
// ordered_set
# include <ext/pb_ds/assoc_container.hpp>
# include <ext/pb_ds/tree_policy.hpp>
using namespace __gnu_pbds;
# define ordered_set tree<int, null_type,less<int>, rb_tree_tag,tree_order_statistics_node_update>
*/
using namespace std;
typedef long long ll;
typedef long double ld;
typedef pair <int, int> pii;
typedef pair <pii, int> ppi;
typedef pair <int, pii> pip;
typedef pair <pii, pii> ppp;
typedef pair <ll, ll> pll;
# define A first
# define B second
# define endl '\n'
# define sep ' '
# define all(x) x.begin(), x.end()
# define kill(x) return cout << x << endl, 0
# define SZ(x) int(x.size())
# define lc id << 1
# define rc id << 1 | 1
# define InTheNameOfGod ios::sync_with_stdio(0);cin.tie(0); cout.tie(0);
#define MP make_pair
ll power(ll a, ll b, ll md) {return (!b ? 1 : (b & 1 ? a * power(a * a % md, b / 2, md) % md : power(a * a % md, b / 2, md) % md));}
const int xn = 1e6 + 10;
const int xm = 1e2 + 10;
const int sq = 320;
const int inf = 1e9 + 10;
const ll INF = 1e18 + 10;
const int mod = 998244353;//1e9 + 7;//998244353;
const int base = 257;
ll n, m, k, st[xn], num[xn], cnt = 1;
vector <int> adj[xn];
void dfs(int v, int par = 0){
num[cnt] = v;
st[v] = cnt++;
for (int u : adj[v]){
if (u != par){
dfs(u, v);
}
}
}
int main(){
InTheNameOfGod;
cin >> n;
for (int i = 0; i < n-1; ++i){
int v, u;
cin >> v >> u;
adj[v].push_back(u);
adj[u].push_back(v);
}
int mx = 0, indmx = -1;
for (int i = 1; i <= n; ++i){
if (int(adj[i].size()) > mx) indmx = i, mx = int(adj[i].size());
}
dfs(indmx);
vector <int> vec;
for (int i = 1; i <= n; ++i){
if (adj[num[i]].size() == 1) vec.push_back(num[i]);
}
int sz = int(vec.size());
cout << (sz+1)/2 << '\n';
if (sz%2 == 1) cout << vec[0] << ' ' << vec[sz-1] << '\n';
for (int i = 0; i < sz/2; ++i) cout << vec[i] << ' ' << vec[sz/2+i] << '\n';
return 0;
}
/*
6
1 2
2 3
2 4
5 4
6 4
8
1 2
2 3
3 4
4 5
3 6
3 7
3 8
*/
