#include <fstream>
#include <vector>
#include <queue>
#include <deque>
#include <iomanip>
#include <stack>
#include <algorithm>
#include <functional>
#include <set>
#define endl '\n';

using namespace std;

const string FISIER = "ciclueuler";
ifstream fin(FISIER + ".in");
ofstream fout(FISIER + ".out");

typedef pair<int, int> pii;
int n, m, cm;
vector<vector<pii>> graph;
vector<bool> viz;
vector<int> grad, ciclu;

void euler(int node) {
	while (graph[node].size()) {
		auto w = graph[node].back();
		graph[node].pop_back();
		if (!viz[w.second]) {
			viz[w.second] = 1;
			euler(w.first);
		}
	}
	ciclu.push_back(node);
}

void solve() {
	euler(1);
	for (int i = 1; i <= n; ++i)
		if (grad[i] % 2 || !viz[i]) {
			fout << -1;
			return;
		}
	for (int i = 0; i < ciclu.size()-1; ++i)
		fout << ciclu[i] << " ";
}

int main()
{
	fin >> n >> m;
	cm = m;
	graph.resize(n + 1);
	viz.resize(m + 1, 0);
	grad.resize(n + 1, 0);
	while (m--) {
		int x, y;
		fin >> x >> y;
		graph[x].push_back({ y, m });
		graph[y].push_back({ x, m });
		grad[x]++;
		grad[y]++;

	}
	solve();
	return 0;
}