#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using P = pair<int, int>;
#define all(x) x.begin(), x.end()
#define rep(i, l, n) for (int i = l; i < (n); ++i)
#define sz(x) (int)x.size()
const char nl = '\n';
const int N = 5e5+10;
vector<int> g[N], A[N];
int cnt[N], idx;
int ex[N];
void calc(int nd, int p) {
cnt[nd] = sz(g[nd]) ==1;
for (auto i: g[nd])
if (i != p)
calc(i, nd),
cnt[nd] += cnt[i];
}
int s = 1;
int dfs(int nd, int p) {
for (auto i: g[nd])
if (i != p && cnt[i] > cnt[s]-cnt[i])return dfs(i, nd);
return nd;
}
void gos(int nd, int p) {
if (sz(g[nd]) == 1)A[idx].push_back(nd), ex[idx] = nd;
for (auto i: g[nd])
if (i != p)gos(i, nd);
}
void solve() {
int n; cin >> n;
int res = n;
rep(i, 0, n-1) {
int u, v; cin >> u >> v;
g[u].push_back(v);
g[v].push_back(u);
if (sz(g[u]) == 2)res -= 1;
if (sz(g[v]) == 2)res -= 1;
}
cout << (res+1)/2 << nl;
if (sz(g[1]) == 1)s = g[s][0];
calc(s, -1);
int lc = dfs(s, -1);
priority_queue<P> pq;
for (auto i: g[lc]) {
gos(i, lc), idx += 1;
pq.push({sz(A[idx-1]), idx-1});
}
while (!pq.empty()) {
P a = pq.top(); pq.pop();
P b = pq.top(); pq.pop();
if (a.first == 0)break;
if (b.first == 0) {
a.first -= 1;
cout << A[a.second].back() << " " << ex[b.second] << nl;
A[a.second].pop_back();
pq.push(a), pq.push(b);
continue;
} else {
cout << A[a.second].back() << " " << A[b.second].back() << nl;
A[a.second].pop_back(), A[b.second].pop_back();
a.first -= 1, b.first -= 1;
pq.push(a), pq.push(b);
}
}
}
int32_t main() {
ios_base::sync_with_stdio(0);
cin.tie(0);
solve();
return 0;
}
