#include <fstream>
#include <algorithm>
#include <stack>
#include <vector>

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

const int NMAX = 1e5 + 2;

std::vector <int> g[NMAX];

void euler()
{
	std::stack <int> st;
	st.push(1);
	std::vector <int> cycle;
	while (!st.empty())
	{
		int node = st.top();
		if (g[node].begin() != g[node].end())
		{
			int new_node = g[node].back();
			g[node].pop_back();
			g[new_node].erase(std::find(g[new_node].begin(), g[new_node].end(), node));
			st.push(new_node);
		}
		else
		{
			st.pop();
			if (!st.empty())
				cycle.push_back(st.top());
		}
	}
	for (auto i : cycle)
		fout << i << " ";
	fout << "\n";
}

int n, x, y, m;

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

	for (int i = 1; i <= n; ++i)
		if (g[i].empty() || g[i].size() & 1)
		{
			fout << "-1\n";
			return 0;
		}

	euler();

	fout.close();
	return 0;
}