#pragma GCC optimize("O2")
#include <fstream>
#include <algorithm>
#include <stack>
#include <vector>
#include <bitset>

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

const int NMAX = 1e5 + 2;

std::vector < std::pair <int, int> > g[NMAX];
std::bitset <5 * NMAX> used;

void euler()
{
	std::stack <int> st;
	st.push(1);
	std::vector <int> cycle;
	while (!st.empty())
	{
		int node = st.top();
		while (!g[node].empty() && used[g[node].back().second])
			g[node].pop_back();

		if (!g[node].empty())
		{
			int new_node = g[node].back().first;
			used[g[node].back().second] = 1;
			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, i });
		g[y].push_back({ x, i });
	}

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

	euler();

	fout.close();
	return 0;
}