#include <fstream>
#include <stack>
#include <vector>
#define NM 100010
#define MM 500010
#define PI pair<int, int>
#define nd first
#define in second

using namespace std;

ifstream f("ciclueuler.in");
ofstream g("ciclueuler.out");

vector<PI> G[NM];

bool F[MM];
int N,M,i,j,a,b;
stack<int> S;
stack<PI> ST;
int DG[NM];
bool V[NM];

void DF (int nod)
{
    V[nod]=1;

    for (vector<PI>::iterator it=G[nod].begin(); it!=G[nod].end(); ++it)
        if (!V[it->nd])
            DF(it->nd);
}

bool Ok ()
{
    DF(1);
    for (i=1; i<=N; i++)
        if ((V[i]==0 && G[i].size()!=0) || DG[i]%2==1)
            return 0;
    return 1;
}

void Euler (int nod)
{
    for (vector<PI>::iterator it=G[nod].begin(); it!=G[nod].end(); ++it)
        if (!F[it->in])
        {
            F[it->in]=1;
            Euler(it->nd);
        }
        g << nod << '\n';

    //S.push(nod);
}

int main ()
{
    f >> N >> M;
    for (i=1; i<=M; i++)
    {
        f >> a >> b;

        DG[a]++;
        DG[b]++;
        G[a].push_back(make_pair(b,i));
        G[b].push_back(make_pair(a,i));
    }

    if (!Ok())
    {
        g << -1 << '\n';

        f.close();
        g.close();
        return 0;
    }

    Euler(1);

    while (S.size()>=2)
    {
        g << S.top() << ' ';
        S.pop();
    }

    g << '\n';
    f.close();
    g.close();
    return 0;
}