#include <bits/stdc++.h>
#define ll long long
#define cin fin
#define cout fout
using namespace std;
	
ifstream fin("ciclueuler.in");
ofstream fout("ciclueuler.out");
int n, m, x, y;
multiset <int> adj[100004];

int main() {
	cin >> n >> m;
	for (int i = 1; i <= m; i++) {
		cin >> x >> y;
		adj[x].insert(y);
		adj[y].insert(x);
	}

	for (int i = 1; i <= n; i++) 
		if (!adj[i].empty() && adj[i].size() % 2) {
			cout << -1;
			return 0;
		}

	stack <int> currNode;
	vector <int> result;
	currNode.push(1);
	while (!currNode.empty()) {
		int node = currNode.top();

		if (adj[node].empty()) {
			result.push_back(node);
			currNode.pop();
		} else {
			int nextNode = *adj[node].begin();
			adj[node].erase(adj[node].begin());
			adj[nextNode].erase(adj[nextNode].find(node));
		
			currNode.push(nextNode);
		}
	}

	for (int i = 0; i < m; i++)
		cout << result[i] << ' ';

	return 0;
}