#include <fstream>
#include <vector>
using namespace std;
ifstream cin ("ciclueuler.in");
ofstream cout ("ciclueuler.out");
vector <int> v[100010];
vector <int> rez;
int a[500010],b[500010],viz[500010];
int euler(int nod)
{
    int muchie,vecin;
    while (v[nod].size()!=0)
    {
        muchie=v[nod].back();
        v[nod].pop_back();
        if (viz[muchie]==0)
        {
            viz[muchie]=1;
            if (a[muchie]==nod)
                vecin=b[muchie];
            else
                vecin=a[muchie];
            euler(vecin);
        }
    }
    rez.push_back(nod);
}
int main()
{
    int n,m,i,ok;
    cin>>n>>m;
    for (i=1; i<=m; i++)
    {
        cin>>a[i]>>b[i];
        v[a[i]].push_back(i);
        v[b[i]].push_back(i);
    }
    ok=1;
    for (i=1; i<=n && ok==1; i++)
        if (v[i].size()%2==1)
        {
            cout<<-1;
            ok=0;
        }
    if (ok==1)
    {
        euler(1);
        for (i=0; i<rez.size()-1; i++)
            cout<<rez[i]<<" ";

    }
    return 0;
}