#include <fstream>
#include <iomanip>
#include <algorithm>
#include <vector>
#include <queue>
#include <set>
#include <stack>
#include <map>
#include <cstring>
#include <climits>
#include <unordered_map>

#define NMAX 100003


using namespace std;

int n,m;
int niv[NMAX];
int start[NMAX];
bool viz[500003];

struct val {
	int vecin, ind;
};

vector<val>graf[NMAX];

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



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

	}


	stack<int>stiv;
	stiv.push(1);
	vector<int>sol;
	while (!stiv.empty())
	{
		int nod = stiv.top();
		if (niv[nod] == 0)
		{
			sol.push_back(nod);
			stiv.pop();
			continue;
		}
		for (int i = start[nod]; i < graf[nod].size(); i++)
		{
			int cMuchie = graf[nod][i].ind;
			int nd = graf[nod][i].vecin;
			start[nod] ++;
			if (!viz[cMuchie])
			{
				viz[cMuchie] = true;
				
				niv[nod]--;
				niv[nd]--;
				stiv.push(nd);
				break;
			}
		}
	}

	if (sol.size() != m + 1)
	{
		fout << "-1";
		return 0;
	}
	for (int i = 0; i < sol.size() - 1; i++)
	{
		fout << sol[i] << " ";
	}
	return 0;
}