#include <fstream>
#include <list>
#include <queue>

using namespace std;

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

int n, m, S[500010], Sol[500010];
bool F[100010];
queue < int > Q;
list < int > L[100010];

void BFS(int nod)
{
    F[nod] = true;
    Q.push(nod);
    while (!Q.empty())
    {
        nod = Q.front();
        Q.pop();
        for (list < int > :: iterator it = L[nod].begin(); it != L[nod].end(); it ++)
        {
            if (!F[*it])
            {
                F[*it] = true;
                Q.push(*it);
            }
        }
    }
}

bool Verif_Euler()
{
    BFS(1);
    for (int i = 1; i <= n; i ++)
    {
        if (L[i].size() & 1 || F[i] == false)
        {
            return 0;
        }
    }
    return 1;
}

void Delet(int i, int nod)
{
    for (list < int > :: iterator it = L[i].begin(); it != L[i].end(); it ++)
    {
        if (*it == nod)
        {
            L[i].erase(it);
            return;
        }
    }
}

void Euler()
{
    S[++S[0]] = 1;
    while (S[0])
    {
        int nod = S[S[0]];
        if (!L[nod].empty())
        {
            S[++S[0]] = L[nod].front();
            Delet(L[nod].front(), nod);
            L[nod].pop_front();
        }
        else
        {
            Sol[++Sol[0]] = nod;
            S[0] --;
        }
    }
}

void Write_Lant_Euler(bool aux)
{
    if (aux)
    {
        Euler();
        for (int i = 1; i < Sol[0]; i ++)
        {
            fout << Sol[i] << ' ';
        }
    }
    else
    {
        fout << "-1";
    }
    fout << '\n';
    fout.close();
}

int main()
{
    fin >> n >> m;
    for (int i = 1, x, y; i <= m; i ++)
    {
        fin >> x >> y;
        L[x].push_back(y);
        L[y].push_back(x);
    }

    Write_Lant_Euler(Verif_Euler());

    return 0;
}