#include <fstream>
#include <vector>
using namespace std;

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

pair <int, int> much[500001];
vector <int> v[100001];
bool ok[100001], okmuch[500001];
int s[500001], rasp[500001];

void dfsconex (int r)
{
	ok[r] = 1;
	int i;
	for (i = 0; i<v[r].size(); i++)
		if (ok[much[v[r][i]].first ^ much[v[r][i]].second ^ r] == 0)
			dfsconex (much[v[r][i]].first ^ much[v[r][i]].second ^ r);
}

int main()
{
	int n, m, i, x, y;
	fin >> n >> m;
	for (i = 1; i<=m; i++)
	{
		fin >> x >> y;
		much[i] = {x, y};
		v[x].push_back(i);
		v[y].push_back(i);
	}
	dfsconex(1);
	for (i = 1; i<=n; i++)
		if (ok[i] == 0 || (v[i].size()&1))
		{
			fout << -1;
			return 0;
		}
	
	s[0] = s[1] = 1;
	while (s[0] > 0)
	{
		x = s[s[0]];
		if (v[x].empty() == 0)
		{
			y = v[x].back();
			v[x].pop_back();
			if (okmuch[y] == 0)
			{
				okmuch[y] = 1;
				s[++s[0]] = x ^ much[y].first ^ much[y].second;
			}
		}
		else
		{
			rasp[++rasp[0]] = x;
			s[0]--;
		}
	}
	for (i = 1; i<=m; i++)
		fout << rasp[i] << ' ';
	return 0;
}