#include <bits/stdc++.h>
#include <set>
#include <map>
#include <unordered_map>
using namespace std;
#define ll long long
#define N (ll)(5e5+5)
#define NP (2097155ll)
#define M ((ll)1e9+7)
#define fi first
#define se second
ll n, ct, r;
vector<ll> v[N];
vector<pair<ll, ll>> ans;
set<pair<ll, ll>> st[N], tmp;
void dfs(ll s, ll p) {
ct++; if (v[s].size() == 1) { st[s].insert({ ct, s }); return; }
for (auto x : v[s]) if (x != p) {
dfs(x, s); if (st[x].size() > st[s].size()) swap(st[x], st[s]);
for (auto y : st[x]) st[s].insert(y);
}
tmp.clear(); for (auto x : st[s]) tmp.insert({ -x.first, x.second });
while (st[s].size() > 2) {
ans.push_back({ (*st[s].begin()).second, (*tmp.begin()).second });
st[s].erase({ -(*tmp.begin()).first, tmp.begin()->second }); tmp.erase(tmp.begin());
tmp.erase({ -st[s].begin()->first, st[s].begin()->second }); st[s].erase(st[s].begin());
}
}
int main() {
#define int ll
ios_base::sync_with_stdio(false), cin.tie(0), cout.tie(0);
cin >> n; ll a, b; for (int i = 1; i < n; i++) cin >> a >> b, v[a].push_back(b), v[b].push_back(a);
for (int i = 1; i <= n; i++) if (v[i].size() > 1) r = i;
dfs(r, 0);
if (st[r].size() == 2) {
pair<ll, ll> c = *st[r].begin(); st[r].erase(st[r].begin());
ans.push_back({ c.second, st[r].begin()->second });
}
else if (st[r].size() == 1) {
ans.push_back({ r, st[r].begin()->second });
}
cout << ans.size() << '\n';
for (auto x : ans) cout << x.first << ' ' << x.second << '\n';
}
