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

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

#define nrn 100005
#define nrm 500005
int n,m;
int nod1[nrm],nod2[nrm];
vector<int>graf[nrn];
int viz[nrm];
vector<int>rez;

void citire()
{
    fin>>n>>m;
    for(int i=1; i<=m; i++)
    {
        int x,y;
        fin>>x>>y;
        nod1[i]=x;
        nod2[i]=y;
        graf[x].push_back(i);
        graf[y].push_back(i);
    }

}

void dfs(int k)
{
    while(!graf[k].empty())
    {
        int muchie=graf[k].back();
        graf[k].pop_back();
        if(viz[muchie]==0)
        {
            viz[muchie]=1;
            int urm;
            if(nod1[muchie]!=k)
            {
                urm=nod1[muchie];
            }
            else
            {
                urm=nod2[muchie];
            }
            dfs(urm);
        }
    }
    rez.push_back(k);
}

void afisare()
{
    for(int i=0; i<rez.size()-1; i++)
    {
        fout<<rez[i]<<" ";
    }
}

int main()
{
    citire();
    for(int i=1; i<=nrn; i++)
    {
        if(graf[i].size()%2==1)
        {
            fout<<"-1";
            fin.close();
            fout.close();
            return 0;
        }
    }

    dfs(1);

    afisare();

    fin.close();
    fout.close();
    return 0;
}