#include<iostream>
#include<fstream>
#include<vector>
#include<stack>
#define NMAX 100010
using namespace std;
vector<int> v[NMAX];
ifstream fin("ciclueuler.in");
ofstream fout("ciclueuler.out");
void citeste(int &nr_noduri, int &nr_muchii){
	int i, x, y;
	fin>>nr_noduri>>nr_muchii;
	for(i=0;i<nr_muchii;++i){
		fin>>x>>y;
		v[x].push_back(y);
		v[y].push_back(x);
	}
}

int esteEulerian(int &nr_noduri){
	int grad, i;
	for(i=0; i<nr_noduri; ++i){
		grad = v[i].size();
		if(grad%2!=0)
			return 0;
	}
	return 1;
}

void determinaCiclu(int &nr_noduri){
	stack<int> stiva;
	vector<int>::iterator it;
	int varf, urm_varf;
	stiva.push(1);
	do{
		varf = stiva.top();
		stiva.pop();
		while(!v[varf].empty()){
			urm_varf = v[varf].back();
			v[varf].pop_back();
			for(it=v[urm_varf].begin(); it != v[urm_varf].end();++it){
				if(*it == varf)
				{
					*it = *(v[urm_varf].end()-1);
					v[urm_varf].pop_back();
					break;
				}
			}
			stiva.push(varf);
			varf = urm_varf;
		}

		
		if(!stiva.empty())
			fout<<stiva.top()<<" ";

	}while(!stiva.empty());
}

int main(){
	int nr_muchii, nr_noduri;
	citeste(nr_noduri, nr_muchii);
	if(esteEulerian(nr_noduri)){
		determinaCiclu(nr_noduri);
	}
	else
		fout<<"-1";

	return 0;
}