#include <bits/stdc++.h>
using namespace std;
#define int ll
#define endl '\n'
#define fast_io ios::sync_with_stdio(0); cin.tie(0); cout.tie(0)
#define pb push_back
#define re resize
#define ff first
#define ss second
#define all(x) (x).begin(), (x).end()
#define loop(i, n) for(int i = 0; i < n; i++)
#define loop1(i, n) for(int i = 1; i <= n; i++)
#define print(x) cout << #x << ": " << x << endl
typedef long long ll;
typedef vector<int> vi;
typedef array<int, 2> ii;
typedef array<int, 3> ti;
typedef vector<ii> vii;
typedef vector<ti> vti;
typedef priority_queue<int> pq;
template<class T> bool ckmin(T&a, T b) { bool B = a > b; a = min(a, b); return B; }
template<class T> bool ckmax(T&a, T b) { bool B = a < b; a = max(a, b); return B; }
const int inf = 1e17;
const int maxn = 5e5+5;
vi adj[maxn];
int leaves;
int sub[maxn];
int node;
void dfs(int u, int p) {
int maxs = 0;
for(auto v : adj[u]) if(v != p) {
dfs(v, u);
sub[u] += sub[v];
ckmax(maxs, sub[v]);
}
ckmax(maxs, leaves - sub[u]);
if(maxs <= (leaves + 1)/2) node = u;
}
void solve_sub(int u, int p, vi& a) {
for(auto v : adj[u]) if(v != p)
solve_sub(v, u, a);
if(adj[u].size() == 1) a.pb(u);
}
void result(int u) {
vi a, b;
for(auto v : adj[u]) {
solve_sub(v, u, a);
while(!a.empty() and !b.empty()) {
int x = a.back(); a.pop_back();
int y = b.back(); b.pop_back();
cout << x << " " << y << endl;
}
if(!a.empty()) swap(a, b);
}
for(auto v : b) {
cout << v << " " << node << endl;
}
}
void solve() {
int n; cin >> n;
loop1(i, n-1) {
int u, v;
cin >> u >> v;
adj[u].pb(v);
adj[v].pb(u);
}
loop1(i, n) sub[i] = 0;
leaves = 0;
loop1(i, n) if(adj[i].size() == 1) {
sub[i] = 1;
leaves++;
}
dfs(1, 1);
cout << (leaves + 1) / 2 << endl;
result(node);
}
signed main() {
fast_io;
int t = 1; //cin >> t;
while(t--)
solve();
cout << flush;
return 0;
}
