#include <bits/stdc++.h>
#define NMAX 100004
#define MMAX 500004

using namespace std;
ifstream fin ("ciclueuler.in");
ofstream fout ("ciclueuler.out");

struct muchie
{
    int x, y;
    bool uz; ///muchia a fost sau nu folosita
};

int n, m;
muchie LM[MMAX];

vector <int> LA[NMAX], sol; ///contine indicii muchiilor care au ca extremitate pe x
stack <int> S;
int vf;

void citire();
void ciclu_eulerien();
void afisare();

int main()
{
    citire();
    ciclu_eulerien();
    afisare();
    return 0;
}

void citire()
{
    int x, y;
    fin >> n >> m;
    for (int i = 1; i <= m; i++)
    {
        fin >> x >> y;
        LA[x].push_back(i);
        LA[y].push_back(i);
        LM[i].x = x;
        LM[i].y = y;
    }
    int i;
    for (i = 1; i <= n; i++)
        if (LA[i].size()%2)
            break;
    if (i <= n)
    {
        fout << -1;
        exit(0);
    }
}

void ciclu_eulerien()
{
    int nod, vecin;
    S.push(1);

    while (!S.empty())
    {
        nod = S.top();
        if (LA[nod].size() == 0)
        {
            sol.push_back(nod);
            S.pop();
        }
        else
        {
            vecin = LA[nod].back();
            LA[nod].pop_back();
            if (LM[vecin].uz == 0)
            {
                LM[vecin].uz = 1;
                if (nod == LM[vecin].x)
                    S.push(LM[vecin].y);
                else
                    S.push(LM[vecin].x);
            }
        }
    }
}

void afisare()
{
    for (int i = 0; i < sol.size() - 1; i++)
        fout << sol[i] << ' ';
}