#include <bits/stdc++.h>
#define NMAX 100002
#define MMAX 500002

using namespace std;
ifstream fin ("ciclueuler.in");
ofstream fout ("ciclueuler.out");

struct muchie
{
    int x, y;
    bool uz;
};

int n, m, poz;
muchie LM[MMAX];
vector<int> LA[NMAX]; ///LA[x] contine indicii muchiilor care il au ca extremitate pe x
int S[MMAX];
int vf;
int sol[MMAX];

void citire();
void ciclu();
bool grade_pare();
void afisare();

int main()
{
    citire();
    if (!grade_pare())
    {
        fout<<-1<<'\n';
        return 0;
    }
    ciclu();
    afisare();
    return 0;
}

void citire()
{
    int i, x, y;
    fin>>n>>m;
    for (i=1; i<=m; i++)
    {
        fin>>x>>y;
        LM[i].x=x;
        LM[i].y=y;
        LM[i].uz=0;
        LA[x].push_back(i);
        LA[y].push_back(i);
    }
}

void ciclu()
{
    int crt, urm;
    S[1]=1;
    vf=1;
    while (vf>0)
    {
        crt=S[vf];
        if (LA[crt].size()==0)
        {
            sol[++poz]=crt;
            vf--;
        }
        else
        {
            urm=LA[crt].back();
            LA[crt].pop_back();
            if (LM[urm].uz==0)
            {
                LM[urm].uz=1;
                if (LM[urm].x==crt)
                    S[++vf]=LM[urm].y;
                else
                    S[++vf]=LM[urm].x;
            }
        }
    }

}

bool grade_pare()
{
    int i;
    for (i=1; i<=n; i++)
        if (LA[i].size()%2)
        return 0;
    return 1;
}

void afisare()
{
    int i;
    if (poz-1!=m)
        fout<<-1<<'\n';
    else
    {
        for (i=1; i<poz; i++)
            fout<<sol[i]<<' ';
        fout<<'\n';
    }
}