#include<fstream>
#include<vector>
#include<stack>
#include<algorithm>
#define NMax 100005
#define MMax 500005
using namespace std;

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

int N,M;
bool Use[NMax],Use_M[MMax],OK;

vector < pair<int,int> > G[NMax];
vector <int> Sol;
stack <int> S;

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

    for(int i = 1 ; i <= M ; ++i)
    {
        int x,y;    fin>>x>>y;
        G[x].push_back(make_pair(y,i));
        G[y].push_back(make_pair(x,i));
    }
}

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

    OK = 1;

    S.push(1);

    while(!S.empty())
    {
        int Nod = S.top();

        if(G[Nod].size())
        {
            int Vecin = G[Nod].back().first;
            int Ind = G[Nod].back().second;
            G[Nod].pop_back();

            if(!Use_M[Ind])
            {
                Use_M[Ind] = 1;
                S.push(Vecin);
            }
        }
        else
        {
            Sol.push_back(S.top());
            S.pop();
        }
    }

}

void Print()
{
    Sol.pop_back();

    for(int i = 0 ; i < (int) Sol.size() ; ++i)
        fout<<Sol[i]<<" ";
    fout<<"\n";
}

int main()
{
    Read();
    Solve();
    if(OK)  Print();

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