#include <fstream>
#include <vector>
#define NMAX 100004
#define MMAX 500007
using namespace std;

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

int n,m ;

struct muchie
{
    int x,y;
    bool uz;///daca muchia a fost sau nu folosita
} LM[MMAX];

vector<int> LA[NMAX];
int S[MMAX];
int vf;
int sol[MMAX];
int poz;

void citire();
void determinare_ciclu();
void afisare();
bool grade_pare();
int main()
{
    citire();
    if(!grade_pare())
    {
        fout<<-1<<'/n';
        return 0;
    }
    determinare_ciclu();
    afisare();
    return 0;
}

void citire()
{
    int x,y;
    fin>>n>>m;
    for(int 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 determinare_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()
{
    for(int i=1; i<=n; i++)
    {
        if(LA[i].size()%2) return 0;
        return 1;
    }
}


void afisare()
{
    if(poz-1!=m) fout<<-1<<endl;
    else
    {

        for(int i=1; i<=poz-1; i++)
            fout<<sol[i]<<" ";
        fout<<endl;
    }
}