#include <iostream>
#include <fstream>
#include <vector>

using namespace std;

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

// pozitia ramasa a fiecarui nod
vector<int> pos;
vector<int> x, y; // nodurile incidente fiecarui muchii
vector<vector<int>> vecini; // vecini
vector<bool> vizMuchie;
vector<int> ciclu;
bool graduriPare()
{
    for (vector<int> &v : vecini)
        if (v.size() % 2 == 1)
            return false;
    return true;
}

void dfsEuler(int nod)
{
    while (pos[nod] < vecini[nod].size())
    {
        int currentMuchie = vecini[nod][pos[nod]];
        pos[nod]++;

        if (!vizMuchie[currentMuchie])
        {
            vizMuchie[currentMuchie] = true;
            dfsEuler(x[currentMuchie] + y[currentMuchie] - nod);
        }
    }

    ciclu.push_back(nod);
}

int main()
{
    int n, m;
    in >> n >> m;


    pos = vector<int>(n, 0);
    vizMuchie = vector<bool> (m, false);
    vecini = vector<vector<int>> (n);

    for (int i = 0; i < m; i++)
    {
        int a, b; in >> a >> b;
        a--; b--;

        x.push_back(a);
        y.push_back(b);
        vecini[a].push_back(i);
        vecini[b].push_back(i);
    }

    if (graduriPare())
    {
        dfsEuler(0);

        for (int i = 0; i < ciclu.size() - 1; i++)
            out << ciclu[i] + 1 << " ";

    }
    else
        out << -1;
    return 0;
}