#include <iostream>
#include <vector>
#include <variant>
using namespace std;
vector<vector<pair<int, int>>> adj;
vector<int> path;
void dfs(int st, int par){
if((par == -1 && adj[st].size() >= 2) || (par!=-1 && adj[st].size()>=3)){
int a = -1, b = -1, c = -1, d = -1;
for(auto i : adj[st]){
if(i.first == par) continue;
if(a == -1){
a = i.second;
b = (i.second%2)?(i.second-1):(i.second+1);
}
else{
c = i.second;
d = (i.second%2)?(i.second-1):(i.second+1);
}
}
vector<int> v = {a, b, c, d, b, a, d, c};
for(auto i : v) path.push_back(i);
return;
}
for(auto i : adj[st]){
if(i.first == par) continue;
path.push_back(i.second);
dfs(i.first, st);
path.push_back(i.second);
}
}
variant<bool, vector<int>> find_journey(int N, int M, vector<int> U, vector<int> V){
adj.assign(N, {});
for(int i = 0; i<M; i++){
adj[U[i]].push_back({V[i], i});
}
if(adj[0].size() == 0) return (bool)0;
if(adj[0].size() > 1){
path.assign(0, 0);
dfs(0, -1);
return path;
}
int curr = adj[0][0].first;
int prev = 0;
while(adj[curr].size() <= 2){
if(adj[curr].size() == 1) return (bool)0;
if(adj[curr][1].first != prev){
prev = curr;
curr = adj[curr][1].first;
continue;
}
prev = curr;
curr = adj[curr][0].first;
}
path.assign(0, 0);
dfs(0, -1);
return path;
}
