#pragma once


#include<iostream>
#include<vector>
#include<fstream>
#include<queue>
#include<algorithm>
#include<unordered_map>


using namespace std;

ifstream fin("ciclueuler.in");
ofstream fout("ciclueuler.out");

int V, E;


class Node {
public:

	unordered_map<int, int> adj; // map pentru ca va trebui sa stergem muchii si se admit bucle si muchii paralele

	void add(int id) {
		adj[id]++;
	}
	
};

vector<Node> nodes;
vector<int> deg;

int checkEulerian() {
	for (int i = 1; i < deg.size(); i++) {
		if (deg[i] % 2 != 0)
			return 0;
	}
	return 1;
}

void rec(int c) {
	int id;
	for (auto x : nodes[c].adj) {
		if (x.second) {
			// delete edge, update degs and recurr

			id = x.first;

			nodes[c].adj[id] --;
			deg[c]--;
			deg[id]--;

			if (id != c) {
				nodes[id].adj[c]--;
			}

			rec(x.first); // this takes the first edge and goes automatically
		}
	}
	// no more edges
	fout << c << " ";
}


void Hierholzer() {
	rec(1);
}

int main() {
	int x, y, w;
	fin >> V >> E;

	nodes.resize(V+1);
	deg.resize(V + 1, 0);

	for (int i = 0; i < E; i++) {
		fin >> x >> y;
		nodes[x].add(y);
		if (x != y)
			nodes[y].add(x);
		deg[x]++;
		deg[y]++;
	}

	if (checkEulerian()) {
		Hierholzer();
	}
	else
		fout << -1;

	return 0;
}