#include <iostream>
#include <fstream>
#include <vector>
#include <stack>
using namespace std;
ifstream ka("ciclueuler.in");
ofstream ki("ciclueuler.out");

const int N_MAX = 100000;
const int M_MAX = 500000;

struct muchie
{
    int index;
    int nr_ordine;
};
vector< vector <muchie> >muchii(N_MAX + 1);
bool folosita[M_MAX + 1], vazut[N_MAX + 1];
int grad[N_MAX + 1];
stack <muchie> stiva;
vector <int> raspuns;

int n, m;
int main()
{
    ka >> n >> m;
    int x, y;
    for(int i = 1; i <= m; i++)
    {
        ka >> x >> y;
        muchie mm;
        mm.index = y;
        mm.nr_ordine = i;
        muchii[x].push_back(mm);
        mm.index = x;
        muchii[y].push_back(mm);
        grad[x]++;
        grad[y]++;
    }
    muchie mm;
    mm.index = x;
    mm.nr_ordine = 0;
    stiva.push(mm);
    while(!stiva.empty())
    {
        int curent = stiva.top().index;
        int f = stiva.top().nr_ordine;
        int c = curent;
        vazut[c] = true;
        stiva.pop();
            for(int i = f; i < muchii[curent].size(); i++)
            {
                if(!folosita[muchii[curent][i].nr_ordine])
                {
                    folosita[muchii[curent][i].nr_ordine] = true;
                    muchie mm;
                    mm.index = curent;
                    mm.nr_ordine = i + 1;
                    stiva.push(mm);
                    curent = muchii[curent][i].index;
                    mm.index = curent;
                    mm.nr_ordine = 0;
                    stiva.push(mm);
                    break;
                }
            }
        raspuns.push_back(c);
    }
    bool euler = true;
    for(int i = 1; i <= n && euler; i++)
    {
        if(!vazut[i] || grad[i]%2 != 0)
            euler = false;
    }
    if(euler)
        for(int i = 0; i < raspuns.size() - 1; i++)
            ki << raspuns[i] << " ";
    else
        ki << -1;
}