#include <fstream>
#include <vector>
#define NMAX 100002
#define MMAX 500002

using namespace std;

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

struct muchie
     {int x, y;
      bool uz; ///va fi 1 daca muchia a fost folositape ciclu
     };
int n, m, poz;
int urm, crt;
muchie LM[MMAX];
vector<int> LA[NMAX];
///LA[x] contine indicii muchiilor care au ca extremitate pe x
int s[MMAX];
int vf;
int sol[MMAX];
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 i;
    int 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 determinare_ciclu()
{
    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]<<" ";
}