#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define sz size()
#define ff first
#define ss second
#define pb push_back
#define pii pair <int, int>
#define dur exit(0)
#define dur1 return(0)
const int N = 5e5 + 5;
int n, uzyn[N];
vector <int> v[N];
pii jog;
void dfs (int x, int par, int h) {
uzyn[x] = h;
for (int i : v[x]) {
if (i == par) continue;
dfs (i, x, h + 1);
}
}
int main () {
// freopen ("input.txt", "r", stdin);
ios::sync_with_stdio(0);cin.tie(0);cout.tie(0);
cin >> n;
for (int i = 1; i < n; ++i) {
int l, r;
cin >> l >> r;
v[l].pb (r);
v[r].pb (l);
}
dfs (1, -1, 1);
vector <pii> kk;
for (int i = 1; i <= n; ++i) {
if ((int)v[i].sz == 1) {
kk.pb ({uzyn[i], i});
}
}
sort (kk.begin(), kk.end());
// reverse (kk.begin(), kk.end());
// for (auto i : kk) {
// cout << i.ff << " " << i.ss << "\n";
// }
// cout << "\n\n";
assert ((int)kk.sz > 1);
cout << ((int)kk.sz + 1) / 2 << "\n";
cout << kk[0].ss << " " << kk.back().ss << endl;
kk.pop_back();
kk.pb ({0, 1});
for (int i = 2; i < (int)kk.sz; i += 2) {
cout << kk[i - 1].ss << " " << kk[i].ss << endl;
}
}
/*
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
*/
