#include <fstream>
#include <vector>
#define nmax 100005
#define mmax 500005
using namespace std;
fstream f1("ciclueuler.in", ios::in);
fstream f2("ciclueuler.out", ios::out);
int n, m, grad[nmax], c[mmax], nrc, stiva[mmax], vf, viz[mmax];
vector <pair<int, int> > v[nmax];
void citire()
{
    int i, x, y;
    f1>>n>>m;
    for(i=1; i<=m; i++)
    {
        f1>>x>>y;
        v[x].push_back({y, i});
        v[y].push_back({x, i});
        grad[x]++;
        grad[y]++;
    }
}
int ok()
{
    int i;
    for(i=1; i<=n; i++)
        if((grad[i]==0)||(grad[i]%2==1)) return 0;
    return 1;
}
void afis()
{
    int i;
    for(i=1; i<nrc; i++)
        f2<<c[i]<<' ';
}
void hier()
{
    int nod, vec, muc;
    vf=1; stiva[vf]=1;
    while(vf!=0)
    {
        nod=stiva[vf];
        if(v[nod].size()) ///daca nodul are vecini
        {
            vec=v[nod].back().first; ///iei primul vecin (cu muchie nevizitata)
            muc=v[nod].back().second;
            v[nod].pop_back();      ///il stergi din lista

            if(!viz[muc])   ///daca muchia nu a fost stearsa
            {
                viz[muc]=1;///o stergi
                vf++;      ///repeti procedeul pentru vecin
                stiva[vf]=vec;
            }
        }
        else ///altfel adaugi nodul la ciclu
        {
            nrc++;
            c[nrc]=nod;
            vf--;///te intorci din recursie
        }
    }
}
int main()
{
    citire();
    if(ok())
    {
        hier();
        afis();
    }
    else f2<<-1;
    return 0;
}