#include <bits/stdc++.h>
#define pb push_back
#define sz(x) (int)x.size()
#define all(x) (x).begin(), (x).end()
#define el "\n"
#define F first
#define S second
using namespace std;
const int N = (1 << 16) + 5;
int st[N];
set <pair <int, int> > G[N];
vector <int> g[N];
vector <int> cur;
set <int> level[N];
int n, a[N], b[N], root;
vector <vector <int> > ans;
bool go(int a, int b, int pr) {
cur[b] = a;
// cerr << sz(G[a]) << " " << sz(g[b]) - (b != root) << el;
if (sz(G[a]) < sz(g[b]) - (b != root)) {
return 0;
}
int it = 0;
bool can = 1;
for (auto x : G[a]) {
if (it < sz(g[b]) && g[b][it] == pr) {
it++;
}
if (it == sz(g[b])) {
break;
}
can &= go(x.S, g[b][it], b);
it++;
}
return can;
}
int main() {
ios::sync_with_stdio(false);
cin.tie(NULL);
cin >> n;
for (int i = 0; i < n; i++) {
cin >> a[i] >> b[i];
g[a[i]].pb(b[i]);
g[b[i]].pb(a[i]);
}
cur.resize(n + 1);
for (int i = 0; i <= n; i++) {
if (sz(g[i]) == 1) {
root = i;
}
}
for (int i = 0; i <= n; i++) {
sort(all(g[i]), [&](int a, int b) {return (sz(g[a]) > sz(g[b]));});
}
for (int i = 0; i < (1 << n); i++) {
level[__builtin_popcount(i)].insert(i);
for (int j = 0; j < n; j++) {
if (i & (1 << j)) {
continue;
}
st[i]++;
}
}
for (int i = 0; i < (1 << n); i++) {
for (int j = 0; j < n; j++) {
if (i & (1 << j)) {
continue;
}
G[i].insert({n - st[i + (1 << j)], (i + (1 << j))});
}
}
for (int lvl = 0; lvl <= n; lvl++) {
for (auto x : level[lvl]) {
while (go(x, root, -1)) {
ans.pb(cur);
for (int i = 0; i <= n; i++) {
int cnt = sz(g[i]) - (i != root);
st[cur[i]] -= cnt;
// cerr << sz(G[cur[i]]) << el;
while (cnt--) {
G[cur[i]].erase(G[cur[i]].begin());
}
// cerr << sz(G[cur[i]]) << el;
if (!st[cur[i]] && __builtin_popcount(cur[i]) > lvl) {
level[__builtin_popcount(cur[i])].erase(cur[i]);
}
}
}
}
}
cout << sz(ans) << el;
for (int i = 0; i < sz(ans); i++) {
for (auto x : ans[i]) {
cout << x << " ";
}
cout << el;
}
}
