#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)
{
    vector <int> :: iterator it;
    for (it = A[nod].begin(); it != A[nod].end(); ++it)
    {
        if (!mc[*it])
        {
            mc[*it] = true;
            Euler(x[*it] + y[*it] - 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;
}