#include<bits/stdc++.h>
#include <variant>
#define MAXN 200007
using namespace std;
int n,m;
vector< pair<int,int> > v[MAXN];
vector<int> path,sol;
int ind[MAXN];
void euler(int x,int start,int cnt,int e){
if(x==start and cnt>0){
path.push_back(e); return;
}
bool fr=true;
for(int i=ind[x];i<v[x].size();i++){
ind[x]++;
if(fr){
fr=false; euler(v[x][i].first,start,cnt+1,v[x][i].second);
}else{
euler(v[x][i].first,x,1,v[x][i].second);
}
i=max(i,ind[x]-1);
}
path.push_back(e);
}
variant<bool, vector<int> > find_journey(int N, int M, vector<int> U, vector<int> V){
n=N; m=M;
for(int i=0;i<m;i++){
U[i]++; V[i]++;
v[U[i]].push_back({V[i],i});
}
euler(1,1,0,-1);
path.pop_back();
reverse(path.begin(),path.end());
if(path.size()!=m)cout<<1/0;
for(int i=0;i<m;i++){
sol.push_back(path[i]);
}
for(int i=m-1;i>=0;i--){
sol.push_back(path[i]);
}
if(sol.empty())return false;
return sol;
}
/*
int main(){
find_journey(6, 7, {0,1,2,2,3,4,5}, {1,2,3,5,4,2,0});
}
*/
