#include<fstream>
#include<vector>
#define NMax 500005
using namespace std;
ifstream fin("ciclueuler.in");
ofstream fout("ciclueuler.out");

int N,M,K;
int U[NMax],V[NMax],Sol[NMax];
bool Use[NMax];
bool ok = 1;

vector <int> G[NMax];

void Read()
{
    fin>>N>>M;

    for(int i = 1 ; i <= M ; ++i)
    {
        fin>>U[i]>>V[i];
        G[U[i]].push_back(i);
        G[V[i]].push_back(i);
    }
}

void DFS(int Nod)
{
    for(int i = 0 ; i < (int) G[Nod].size() ; ++i)
    {
        int Vecin = G[Nod][i];
        if(!Use[Vecin])
        {
            Use[Vecin] = 1;
            DFS(U[Vecin] + V[Vecin] - Nod);
        }
    }
    Sol[++K] = Nod;
}

void Print()
{
    for(int i = 1 ; i < K ; ++i)
        fout<<Sol[i]<<" ";
    fout<<"\n";
}

int main()
{
    Read();

    for(int i = 1 ; i <= N ; ++i)
        if(G[i].size() % 2)
        {
            fout<<-1;
            return 0;
        }

    DFS(1);
    Print();

    fin.close();
    fout.close();
    return 0;
}