#include <fstream>
#include <utility>
#include <vector>
#include <tuple>
#include <stack>
using namespace std;

typedef vector<int> VI;
typedef pair<int, int> PI;
typedef vector<PI> VP;
typedef vector<VP> VVP;
typedef vector<bool> VB;
typedef VP::iterator Iter;

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

VVP G;
VB v;
VI ce;
int n, m;

void CitesteDate();
void CicluEuler(int x);
bool EsteEulerian();
void ScrieCiclu();

int main()
{
	if (!EsteEulerian())
		fout << -1;
	else
	{
		CicluEuler(1);
		ScrieCiclu();
	}
	
	return 0;
}

void CicluEuler(int x)
{
	vector<Iter> p(n + 1);
	for (int nod = 1; nod <= n; ++nod)
		p[nod] = G[nod].begin();
		
	stack<int> stk;
	stk.push(x);
	int y, e;
	
	while (!stk.empty())
	{
		x = stk.top();
		if (p[x] == G[x].end())
		{
			ce.emplace_back(x);
			stk.pop();
		}
		
		else
		{
			tie(e, y) = *p[x]++;
			if (v[e]) continue;
			v[e] = true;
			stk.push(y);
		}
	}
}	

void CitesteDate()
{
	fin >> n >> m;
	G = VVP(n + 1);
	v = VB(m + 1);
	
	int x, y;
	for (int i = 1; i <= m; ++i)
	{
		fin >> x >> y;
		G[x].emplace_back(i, y);
		G[y].emplace_back(i, x);
	}
}

void ScrieCiclu()
{
	for (int x : ce)
		fout << x << ' ';
}

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