#include <fstream>
#include <vector>
#define NMAX 100002
using namespace std;
ifstream fin("ciclueuler.in");
ofstream fout("ciclueuler.out");

struct muchie
{
    int x, y;
    bool uz;
};
muchie LM[NMAX];
vector <int>LA[NMAX];
int n, m, poz;
int S[NMAX];
int vf;
int sol[NMAX];


void citire();
void determinare_ciclu();
void afisare();
bool grade_pare();

int main()
{
    citire();
    determinare_ciclu();
    afisare();
    return 0;
}

void citire()
{
    int i, 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()
{ 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()
{ 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]<<" ";
     fout<<'\n';
    }
}