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

ifstream f("ciclueuler.in");
ofstream g("ciclueuler.out");

int n, m, x[500500], y[500500], sol[500500];
bool mc[500500];
vector <int> A[100100];

inline void Euler(int nod)
{	for (int i=0; i<A[nod].size(); i++)
    {
        if (!mc[A[nod][i]])
        {
            mc[A[nod][i]] = true;
            Euler(x[A[nod][i]] + y[A[nod][i]] - nod);
        }
    }
    sol[++sol[0]] = nod;
}

int main()
{
    f >> n >> m;
    for (int i = 1; i <= m; ++i)
    {
        f >> x[i] >> y[i];
        A[x[i]].push_back(i);
        A[y[i]].push_back(i);
    }

    for (int i = 1; i <= n; ++i)
        if (A[i].size() % 2 == 1)
        {
            g << "-1\n";
            g.close();
            return 0;
        }

    Euler(1);
    for (int i = 1; i <= sol[0]; ++i)
        g << sol[i] << ' ';

    g << '\n';
    g.close();
    return 0;
}