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


typedef std::vector< std::pair< int, int > >::iterator iter;


const int MAXN = 100005;
const int MAXM = 500005;
std::ifstream f("ciclueuler.in");
std::ofstream g("ciclueuler.out");
int n, m;
std::vector< std::pair< int, int > > G[MAXN];
std::bitset<MAXM> viz;
std::stack<int> st;
std::vector<int> sol;


bool iseuler()
{
	for (int i = 1; i <= n; i++) {
		if (G[i].size() % 2 != 0) {
			return false;
		}
	}
	return true;
}


void euler()
{
	st.push(1);
	while (!st.empty()) {
		int nd = st.top();

		bool breaked = false;
		for (iter it = G[nd].begin(); it != G[nd].end() && !breaked; it++) {
			if (viz[it->second] == true) {
				continue;
			}
			viz[it->second] = true;
			st.push(it->first);
			breaked = true;
		}
		if (!breaked) {
			sol.push_back(nd);
			st.pop();
		}
	}
}


int main()
{
	f >> n >> m;
	for (int i = 1, x, y; i <= m; i++) {
		f >> x >> y;
		G[x].push_back(std::make_pair(y, i));
		G[y].push_back(std::make_pair(x, i));
	}

	if (!iseuler()) {
		g << -1 << std::endl;
		f.close();
		g.close();
		return 0;
	}


	euler();
	for (int i = 1; i < sol.size(); i++) {
		g << sol[i] << ' ';
	}
	g << std::endl;


	//system("pause");
	f.close();
	g.close();
	return 0;
}