#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];
bool vis[MAXN];
void euler(int x,int e){
for(int i=ind[x];i<v[x].size();i++){
ind[x]++;
if(v[x][i].second<0 and !vis[-v[x][i].second]){
swap(v[x][i],v[x][v[x].size()-1]); i--; continue;
}
euler(v[x][i].first,v[x][i].second);
i=max(i,ind[x]-1);
}
path.push_back(e);
}
vector<int> ll,rr;
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]++;
if(U[i]<V[i]){
ll.push_back(i);
}else{
rr.push_back(i);
}
v[U[i]].push_back({V[i],i});
}
if(n==2){
if(int(ll.size())<2 or int(rr.size())<1)return false;
sol={ll[0],rr[0],ll[1],ll[0],rr[0],ll[1]};
return sol;
}
for(int i=0;i<m;i++){
v[V[i]].push_back({U[i],-i});
}
euler(1,-1);
path.pop_back();
reverse(path.begin(),path.end());
for(int i=0;i<path.size();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});
}
*/
