#include <bits/stdc++.h>

using namespace std;

const int NMAX = 500005;

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

int src[NMAX], dest[NMAX];
unsigned int poz[NMAX] = {0}; // poz[i] - pozitia unde am ramas in lista de adiacenta L[i]
int N, M;
bool viz[NMAX];
vector<int> G[NMAX], q;

void Citire()
{
    fin >> N >> M;
    for (int i = 1; i <= M; i++)
    {
        fin >> src[i] >> dest[i];
        G[src[i]].push_back(i);
        G[dest[i]].push_back(i);
    }
}

bool Conditie_grad_par()
{
    for (int i = 1; i <= N; i++)
        if (G[i].size() % 2 == 1)
            return false;

    return true;
}

void DFS(int nod)
{
    while (poz[nod] < G[nod].size())
    {
        int k = G[nod][poz[nod]++];
        if (!viz[k])
        {
            viz[k] = true;
            DFS(dest[k]);
        }
    }
    q.push_back(nod);
}

void Ciclu_Eulerian()
{
    if (!Conditie_grad_par()) {
        fout << "-1" << endl;
    }
    else {
        DFS(1);
        for (auto nod : q)
            fout << nod << " ";
        fout << endl;
    }
}

int main()
{
    Citire();
    Ciclu_Eulerian();
    fin.close();
    fout.close();
    return 0;
}