#include <fstream>
#include <vector>
#include <queue>
using namespace std;
ifstream cin("ciclueuler.in");
ofstream cout("ciclueuler.out");
int n,m,i,j,x,y,nod,next,aux;
vector <int> graf[100001],rasp;
vector <int> ::iterator it;
queue <int> coada;
bool eulerian=true;
int sterge(int nod, int nod2)
{
    for(int i=0; i<graf[nod].size(); i++)
        if(graf[nod][i]==nod2)
        {
            graf[nod].erase(graf[nod].begin()+i);
            return 0;

        }

}
int main()
{
    cin>>n>>m;
    for(i=1; i<=m; i++)
    {
        cin>>x>>y;
        graf[x].push_back(y);
        graf[y].push_back(x);
    }
    coada.push(1);
    while(!coada.empty())
    {
        nod=coada.front(); coada.pop();
        for(i=0; i<graf[nod].size(); i++)
        {
            aux++;
            next=graf[nod][i];
            graf[nod].erase(graf[nod].begin()+i);
            sterge(next,nod);
            coada.push(next);
        }
        rasp.push_back(nod);
    }
    if(eulerian)
        for(it=rasp.begin(); it!=rasp.end(); it++)
            cout<<*it<<" ";
    else
        cout<<"-1";


}