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

using namespace std;

const int N = 1e5;
const int M = 5e5;

struct muchie
{
    int x, y;
};

muchie e[M];
bitset <M> sters;
vector <int> a[N+1];
vector <int> ciclul;
int ultimul[N+1];

int celalalt(muchie m, int x)
{
    return (m.x + m.y - x);
}

void euler(int x)
{
    while (ultimul[x] < (int)a[x].size())
    {
        int ind = a[x][ultimul[x]++];
        if (!sters[ind])
        {
            int y = celalalt(e[ind], x);
            sters[ind] = 1;
            euler(y);
        }
    }
    ciclul.push_back(x);
}

bool toate_gradele_pare(int n)
{
    for (int i = 1; i <= n; i++)
        if (a[i].size() % 2 != 0)
            return false;

    return true;
}

int main()
{
    ifstream fin("ciclueuler.in");
    ofstream fout("ciclueuler.out");

    int n, m;
    fin >> n >> m;

    for (int i = 0; i < m; i++)
    {
        fin >> e[i].x >> e[i].y;
        a[e[i].x].push_back(i);
        a[e[i].y].push_back(i);
    }
    euler(e[0].x);
    if (!toate_gradele_pare(n) || (int)ciclul.size() != m + 1)
        fout << -1;
    else
        for (int i = 0; i < (int)ciclul.size() - 1; i++)
            fout << ciclul[i] << " ";

    return 0;
}