#include "islands.h"
#include "bits/stdc++.h"
using namespace std;
#define ii pair<int,int>
const int MAX_N=1e5+5;
vector<ii> adj[MAX_N];
vector<bool> vis(MAX_N,false);
vector<int> path,res;
int piv=-1;
void dfs(int u){
if(piv!=-1) return;
vis[u]=true;
if(adj[u].size()>=2 && u){
piv=u;
int a=adj[u][0].second,b=adj[u][1].second;
vector<int> aux={a,a+1,b,b+1,a+1,a,b+1,b};
for(int i: path) res.push_back(i);
for(int i: aux) res.push_back(i);
for(int i=path.size()-1;i>=0;i--) res.push_back(path[i]);
return;
}
for(auto v: adj[u]){
if(vis[v.first]) continue;
path.push_back(v.second);
dfs(v.first);
path.pop_back();
}
}
variant<bool, vector<int>> find_journey(int n, int m, vector<int> u, vector<int> v){
for(int i=0;i<m;i+=2)
adj[u[i]].push_back({v[i],i});
dfs(0);
if(piv==-1) return false;
return res;
}
