#include <bits/stdc++.h>
using namespace std;
ifstream f("ciclueuler.in");
ofstream g("ciclueuler.out");

vector <int> a[100005];
vector <int> stiv; //pot fi prea multe noduri in ciclu , lucru care ar sparge stiva daca am amborda problema in mod recursiv
int i,n,m,x,y,afis;

void erase_edge (int nod , int vecin)
{
    int h,nrvecini;
    nrvecini=a[nod].size();
    for (h=0;h<nrvecini;h++)
     if (a[nod][h]==vecin)
     {
         a[nod].erase(a[nod].begin()+h);
         return;
     }
}

void euler ()
{
    int vecin,nod;
    stiv.push_back(1);
    while (stiv.size())
    {
        nod=stiv.back();
        if (a[nod].size())
        {
            vecin=a[nod].back();
            a[nod].pop_back();
            erase_edge(vecin,nod);
            stiv.push_back(vecin);
        }
        else
        {

            g<<nod<<" ";
            stiv.pop_back();
        }
    }
}

int main()
{
    f>>n>>m;
    for (i=1;i<=m;i++)
    {
        f>>x>>y;
        a[x].push_back(y);
        a[y].push_back(x);
    }

    for (i=1;i<=n;i++)
     if (a[i].size()%2 || a[i].empty())
      {
          g<<"-1";
          return 0;
      }

    euler();
    return 0;
}