/*
ID: agageld1
LANG: C++17
TASK:
*/
#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define N 600005
#define ff first
#define ss second
#define pb push_back
#define sz(s) (int)s.size()
#define rep(c, a, b) for(c = a; c <= b; c++)
//mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
ll n, t, out[N], par[N];
vector <int> v[N], ans;
int main () {
ios::sync_with_stdio(0);cin.tie(0);
cin >> n;
for(int i = 1; i < n; i++) {
int x, y;
cin >> x >> y;
par[x] = y;
v[x].pb(y);
v[y].pb(x);
out[x]++;
}
for(int i = 1;i<=n;i++) {
if(sz(v[i]) == 1) ans.pb(i);
}
cout << (sz(ans) + 1) / 2 << '\n';
for(int i = 0; i < sz(ans) - 1; i++) {
cout << ans[i] << " " << ans[i+1] << '\n';
i++;
}
if(sz(ans) % 2) {
for(int i = 1; i <= n; i++) {
if(par[ans[sz(ans)-1]] != i && i != ans[sz(ans) - 1]) {
cout << i << " " << ans[sz(ans) - 1] << '\n';
break;
}
}
}
}
