#include <bits/stdc++.h>
using namespace std;

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

int n, m;
vector<pair<int, int> > g[100005];
bool v[100005], ve[500005];
vector<int> cycle;

void dfs(int x) {
	v[x] = true;
	for(auto next: g[x])
		if(!v[next.first])
			dfs(next.first);
}

void euler(int x) {
	while(g[x].size()) {
		auto next = g[x].back();
		g[x].pop_back();

		if(ve[next.second]) continue;
		ve[next.second] = true;
		euler(next.first);
	}
	cycle.push_back(x);
}

int main() {
	fin >> n >> m;
	while(m--) {
		int u, v;
		fin >> u >> v;
		g[u].push_back({v, m});
		g[v].push_back({u, m});
	}

	dfs(1);
	for(int i = 1; i <= n; i++)
		if(g[i].size()&1 || !v[i]) {
			fout << -1;
			return 0;
		}
	euler(1);
	for(auto x: cycle) fout << x << ' ';
}