#include <list>
#include <fstream>
#include <vector>
#include <iostream>
#include <algorithm>
#include <queue>
#include <stack>
using namespace std;

queue <int> Q;
vector <bool> viz;
vector <int> G;
stack <int> sol;
vector <list <int> > g;
int n, m;
bool res = 1;

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

void bfs(int x) {
	Q.push(x);
	viz[x] = 1;
	while (Q.size()) {
		x = Q.front();
		Q.pop();
		for (list <int> :: iterator it = g[x].begin(); it != g[x].end(); ++it)
			if (!viz[*it]) {
				viz[*it] = 1;
				Q.push(*it);
			}
	}
}

bool grad() {
	for (int i = 1; i <= n; ++i)
		if (G[i] & 1 || (!viz[i] && G[i]))
			return 0;
	return 1;
}

void euler(int x) {
	sol.push(x);
	while (sol.size()) {
		x = sol.top();
		if (!g[x].size()) {
			fout << x << " ";
			sol.pop();
		}
		else {
			int y = *g[x].begin();
			g[x].erase(g[x].begin());
			list <int> :: iterator it = g[y].begin();
			while (it != g[y].end() && *it != x)
				++it;
			g[y].erase (it);
			sol.push(y);
		}
	}
}

int main() {
	fin >> n >> m;
	viz.resize(n+1);
	G.resize(n+1);
	g.resize(n+1);
	while (m--) {
		int x, y;
		fin >> x >> y;
		if (x != y)
			G[x]++, G[y]++;
		g[x].push_back (y);
		g[y].push_back (x);
	}
	fin.close();
	bfs(1);
	res = grad(); 
	if (res)
		euler(1);
	else
		fout << -1;
	fout.close();
}