#include <fstream>
#include <vector>
//#include <utility>
#define NX 100001
#define MX 500001
using namespace std;

int n,m;
vector< pair<int, int> > v[NX];
bool viz[MX];
vector<int> drum;

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

void citire()
{
    int i,x,y;
    pair<int, int> muchie;
    fin>>n>>m;
    for(i=1; i<=m; i++)
    {
        fin>>x>>y;
        muchie.first = y;
        muchie.second = i;
        v[x].push_back(muchie);

        muchie.first = x;
        v[y].push_back(muchie);
    }
}

void DFS(int i)
{
    if(v[i].empty())
    {
        drum.push_back(i);
        return;
    }

    pair<int, int> e;
    while(!v[i].empty())
    {
        e = v[i].back();
        v[i].pop_back();

        if(!viz[e.second])
        {
            viz[e.second] = 1;
            m--;
            DFS(e.first);
        }
    }

    drum.push_back(i);
}

int main()
{
    citire();
    DFS(1);

    //fout<<drum.size()<<'\n';
    //drum.clear();

    if(m > 0)
    {
        fout<<-1;
    }
    else
    {
        drum.pop_back();
        while(!drum.empty())
        {
            fout<<drum.back()<<' ';
            drum.pop_back();
        }
    }

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