#include <fstream>
#include <vector>
#include <bitset>
#include <stack>
using namespace std;
ifstream fin ("ciclueuler.in");
ofstream fout ("ciclueuler.out");
int n,m,i,x,y,k,nod,sol[500005];
vector <pair <int,int>> v[100001];
bitset <500001> viz;
stack <int> s;
void dfs ()
{
    s.push (1);
    while (!s.empty ())
    {
        nod=s.top ();
        while (!v[nod].empty ()&&viz[v[nod].back ().second])
            v[nod].pop_back ();
        if (!v[nod].empty ())
        {
            int vecin=v[nod].back ().first;
            int poz=v[nod].back ().second;
            v[nod].pop_back ();
            viz[poz]=1;
            s.push (vecin);
        }
        else
        {
            sol[++k]=nod;
            s.pop ();
        }
    }
}
int main()
{
    fin>>n>>m;
    for (i=1; i<=m; i++)
    {
        fin>>x>>y;
        v[x].push_back (make_pair (y,i));
        v[y].push_back (make_pair (x,i));
    }
    for (i=1; i<=n; i++)
    {
        if (v[i].size ()%2!=0)
        {
            fout<<-1;
            return 0;
        }
    }
    dfs ();
    if (viz.count ()!=m)
    {
        fout<<-1;
        return 0;
    }
    for (i=1; i<k; i++)
        fout<<sol[i]<<" ";
    return 0;
}