#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace std;
using namespace __gnu_pbds;
template<typename T> using Tree = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
typedef long long int ll;
typedef long double ld;
typedef pair<int,int> pii;
typedef pair<ll,ll> pll;
#define fastio ios_base::sync_with_stdio(false); cin.tie(NULL)
#define pb push_back
#define endl '\n'
#define sz(a) (int)a.size()
#define setbits(x) __builtin_popcountll(x)
#define ff first
#define ss second
#define conts continue
#define ceil2(x,y) ((x+y-1)/(y))
#define all(a) a.begin(), a.end()
#define rall(a) a.rbegin(), a.rend()
#define yes cout << "Yes" << endl
#define no cout << "No" << endl
#define rep(i,n) for(int i = 0; i < n; ++i)
#define rep1(i,n) for(int i = 1; i <= n; ++i)
#define rev(i,s,e) for(int i = s; i >= e; --i)
#define trav(i,a) for(auto &i : a)
template<typename T>
void amin(T &a, T b) {
a = min(a,b);
}
template<typename T>
void amax(T &a, T b) {
a = max(a,b);
}
#ifdef LOCAL
#include "debug.h"
#else
#define debug(...) 42
#endif
/*
*/
const int MOD = 1e9 + 7;
const int N = 1e5 + 5;
const int inf1 = int(1e9) + 5;
const ll inf2 = ll(1e18) + 5;
#include "islands.h"
vector<pii> adj[N];
vector<bool> vis(N), recstack(N);
bool cyc = false;
void dfs1(int u){
vis[u] = 1;
recstack[u] = 1;
for(auto [v,id] : adj[u]){
if(vis[v]){
if(recstack[v]){
cyc = true;
}
}
else{
dfs1(v);
}
}
recstack[u] = 0;
}
bool line = true;
vector<pii> par(N,{-1,-1});
vector<bool> good(N);
void dfs2(int u, int p){
vis[u] = 1;
int d = sz(adj[u])-(p != -1);
if(d >= 2){
good[u] = 1;
line = false;
}
for(auto [v,id] : adj[u]){
if(v == p or vis[v]) conts;
par[v] = {u,id};
dfs2(v,u);
}
}
std::variant<bool, std::vector<int>> find_journey(
int n, int m, std::vector<int> U, std::vector<int> V) {
rep(i,m){
int u = U[i], v = V[i];
adj[u].pb({v,i});
}
dfs2(0,-1);
if(line){
return false;
}
vector<int> ans;
rep(i,n){
if(!good[i]) conts;
bool ok = true;
int u = i;
vector<int> edges;
while(true){
auto [p,pid] = par[u];
if(p == -1) break;
edges.pb(pid);
u = p;
if(good[u]){
ok = false;
break;
}
}
if(!ok) conts;
vector<int> seq;
vector<int> v1,v2; // sz(v1) = 2, sz(v2) = 1
int adj_node = -1;
for(auto [v,id] : adj[i]){
if(v == par[i].ff) conts;
v1.pb(id);
adj_node = v;
}
assert(adj_node != -1);
for(auto [v,id] : adj[adj_node]){
if(v == i){
v2.pb(id);
break;
}
}
assert(!v2.empty());
assert(sz(v1) >= 2);
while(sz(v1) > 2) v1.pop_back();
rep(iter,3){
int x = v1[0];
v1.erase(v1.begin());
v2.pb(x);
int y = v2[0];
v2.erase(v2.begin());
v1.pb(y);
seq.pb(x), seq.pb(y);
}
ans = edges;
reverse(all(ans));
trav(x,seq) ans.pb(x);
trav(x,edges) ans.pb(x);
return ans;
}
return true;
}
