#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(int nod);
void afisare();

int main()
{
    citire();
    ciclu(1);
    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(int nod)
{
    if (LA[nod].size() == 0)
        sol.push_back(nod);
    else
    {
        while (!LA[nod].empty())
        {
            int vecin = LA[nod].back();
            LA[nod].pop_back();
            if (LM[vecin].uz == 0)
            {
                LM[vecin].uz = 1;
                if (LM[vecin].x == nod)
                    ciclu(LM[vecin].y);
                else
                    ciclu(LM[vecin].x);
            }
        }

        if (LA[nod].size() == 0)
            sol.push_back(nod);
    }
}

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