#include "pch.h"
#include <iostream>
#include <fstream>
#include <vector>
#include <stack>

using namespace std;

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

int n, m, k;
int sol[500005];
int f[500005];
vector <pair<int, int>> graph[100005];

void euler(int a)
{
	stack <int> stk;
	stk.push(1);

	while (stk.size()) {
		int node = stk.top();

		if (!graph[node].size()) {
			stk.pop();
			sol[++k] = node;
			continue;
		}
		
		int neighNode = graph[node].back().first;
		int edge = graph[node].back().second;
		graph[node].pop_back();

		if (!f[edge]) {
			f[edge] = 1;
			stk.push(neighNode);
		}
	}
}


int main()
{
	ios::sync_with_stdio(false);
	fin.tie(0); fout.tie(0);

	fin >> n >> m;
	for (int i = 1; i <= m; ++i) {
		int x, y;
		fin >> x >> y;
		graph[x].push_back({ y, i });
		graph[y].push_back({ x, i });
	}

	for (int i = 1; i <= n; ++i) {
		if (graph[i].size() == 0 || graph[i].size() % 2) {
			fout << -1 << '\n';
			return 0;
		}
	}

	euler(1);

	for (int i = 1; i < k; ++i) fout << sol[i] << " ";
}