#include <bits/stdc++.h>
using namespace std;

/**

*/
ifstream fin("ciclueuler.in");
ofstream fout("ciclueuler.out");

int n, m;
int sol[500005], p;
int viz[500005];
/// viz[i] = 1, daca muchia (st[i],dr[i]) a fost parcursa
/// viz[i] = 0, daca muchia (st[i],dr[i]) nu a fost folosita
int st[500005], dr[500005];
/// st[i], dr[i] = muchia i, i=1..m
vector<int> h[100002];

void Citire()
{
    int i;
    fin >> n >> m;
    for (i = 1; i <= m; i++)
    {
        fin >> st[i] >> dr[i];
        h[st[i]].push_back(i);
        h[dr[i]].push_back(i);
    }
}

/// ret. 1 daca gradele tuturor nodurilor sunt pare
int ToatePare()
{
    for (int i = 1; i <= n; i++)
        if (h[i].size() % 2 == 1) return 0;
    return 1;
}

void Euler(int k)
{
    for (int i : h[k])
        if (viz[i] == 0)
        {
            viz[i] = 1;
            ///if (k == st[i]) Euler(dr[i]);
            ///else Euler(st[i]);
            Euler(st[i] + dr[i] - k);
        }
    sol[++p] = k;
}

void Afis()
{
    for (int i = 1; i < p; i++)
        fout << sol[i] << " ";
}

int main()
{
    Citire();
    if (ToatePare() == 0) fout << "-1\n";
    else
    {
        Euler(1);
        Afis();
    }
    fout.close();
    return 0;
}