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

using namespace std;

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

const int maxn = 100005;

int n, m;
vector <int> g[maxn];

inline void euler(int stnode) {
	stack <int> st;
	st.push(stnode);
	vector <int> cycle;
	while (!st.empty()) {
		int node = st.top();
		if (g[node].size()) {
			int newnode = g[node].back();
			g[node].pop_back();
			g[newnode].erase(find(g[newnode].begin(), g[newnode].end(), node));
			st.push(newnode);
		}
		else {
			st.pop();
			if (!st.empty())
				cycle.push_back(node);
		}
	}
	for (auto it : cycle)
		fout << it << ' ';
}

int main() {
	fin >> n >> m;
	for (int i = 1; i <= m; ++i) {
		int x, y;
		fin >> x >> y;
		g[x].push_back(y);
		g[y].push_back(x);
	}
	for (int i = 1; i <= n; ++i) {
		if (!g[i].size() || g[i].size() % 2 == 1) {
			fout << "-1\n";
			return 0;
		}
	}
	euler(1);
}