#include <algorithm>
#include <iostream>
#include <list>
#include <fstream>
#include <vector>

class Graph {
public:
	Graph(int n) : edge(n) {}

	void add_edge(int u, int v) {
		edge[u].push_back(v);
		edge[v].push_back(u);
	}

	std::vector<int> compute_euler() {
		std::vector<int> euler;
		for (std::list<int>& el : edge)
			if (el.size() % 2 == 1)
				return euler; // Euler circuit does not exist.

		std::list<int> st;
		st.push_back(0);
		while (st.size() > 0) {
			int v = st.back();
			if (edge[v].size() > 0) {
				int u = edge[v].front();
				edge[v].pop_front();
				edge[u].erase(std::find(edge[u].begin(), edge[u].end(), v));
				st.push_back(u);
			} else {
				if (st.size() > 1) // Don't print last element again.
					euler.push_back(v);
				st.pop_back();
			}
		}

		return euler;
	}

private:
	std::vector<std::list<int>> edge;
};

int main() {
	std::ifstream in("ciclueuler.in");
	std::ofstream out("ciclueuler.out");

	int n, m;
	in >> n >> m;

	Graph g(n);
	for (int i = 0; i < m; i++) {
		int u, v;
		in >> u >> v;
		g.add_edge(u - 1, v - 1);
	}

	std::vector<int> euler = g.compute_euler();
	if (euler.size() == 0) {
		out << "-1\n";
	} else {
		for (int x : euler)
			out << x + 1 << " ";
		out << "\n";
	}

	return 0;
}