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

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

int N, M;
map<int, vector<int>> G;
vector<int> sol;
vector<pair<int, int>> edges;
map<int, bool> visited;

void Euler()
{
	stack<int> stack;

	stack.push(1);
	while (!stack.empty())
	{
		int node = stack.top();
		if (G[node].size())
		{
			int next = G[node].back();
			G[node].pop_back();
			if (visited[next])
			{
				if (edges[next].first == node)
					stack.push(edges[next].second);
				else
					stack.push(edges[next].first);
				visited[next] = false;
			}
		}
		else
		{
			fout << node << " ";
			stack.pop();
		}
	}
}

int main()
{
	fin >> N >> M;
	for (int i = 0; i < M; i++)
	{
		int x, y;
		fin >> x >> y;
		G[x].push_back(i);
		G[y].push_back(i);
		edges.push_back({ x, y });
		visited[i] = true;
	}

	for (int i = 1; i <= N; i++)
		if (G[i].size() % 2 == 1)
		{
			fout << "-1";
			return 0;
		}
	Euler();


	return 0;
}