#include <bits/stdc++.h>
using namespace std;
const int nmax = (1 << 16) + 1;
vector<pair<int, int>> adj[nmax];
int timer = 0;
int to[nmax];
void dfs_init(int i, int tata = -1) {
for (auto &[it, c] : adj[i]) {
if (it == tata) {
continue;
}
c = timer++;
dfs_init(it, i);
}
}
bool kil = 0;
set<pair<int, int>> viz;
set<pair<int, int>> aux;
void dfs(int i, int val, int tata = -1) {
for (auto &[it, c] : adj[i]) {
if (it == tata) {
continue;
}
int v1 = val, v2 = val ^ (1 << c);
if (viz.find({min(v1, v2), max(v1, v2)}) != viz.end()) {
kil = 1;
}
aux.insert({min(v1, v2), max(v1, v2)});
to[it] = val ^ (1 << c);
dfs(it, (val ^ (1 << c)), i);
}
}
int32_t main() {
ios_base::sync_with_stdio(false);
cin.tie(nullptr);
cout.tie(nullptr);
int n;
cin >> n;
for (int i = 1; i <= n; i++) {
int a, b;
cin >> a >> b;
adj[a].push_back({b, 0});
adj[b].push_back({a, 0});
}
dfs_init(0);
cout << (1 << (n - 1)) << '\n';
for (int i = 0; i < (1 << n); i++) {
kil = 0;
aux.clear();
to[0] = i;
dfs(0, i);
if (kil) {
continue;
}
for (auto it : aux) {
viz.insert(it);
}
for (int j = 0; j <= n; j++) {
cout << to[j] << " ";
}
cout << '\n';
}
return 0;
}
