#include <fstream>
#include <vector>
#include <stack>

using namespace std;

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

const int NMax = 1e5, MMax = 5e5;

int N, M;

struct str{int x, y;} V[MMax + 5];

vector <int> G[NMax + 5], Sol;

stack <int> S;

bool Viz[NMax + 5], Use[MMax + 5];

int Vec(int Nod, int m)
{
    if(Nod == V[m].x) return V[m].y;

    return V[m].x;
}

void DFS(int Nod)
{
    Viz[Nod] = 1;

    for(auto m : G[Nod])
    {
        int Vecin = Vec(Nod, m);

        if(Viz[Vecin] == 0)
            DFS(Vecin);
    }
}

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

    DFS(1);

    for(int i = 1; i <= N; i++)
        if(Viz[i] == 0)
            return 0;

    return 1;
}

void Solve()
{
    S.push(1);

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

        if(!G[Nod].empty())
        {
            int m = G[Nod].back(); G[Nod].pop_back();

            if(!Use[m])
                Use[m] = 1, S.push(Vec(Nod, m));
        }
        else
            Sol.push_back(Nod), S.pop();
    }
    for(int i = 0 ; i < Sol.size() - 1; i++)
        fout << Sol[i] << " ";

    fout << '\n';
}

int main()
{
    fin >> N >> M;

    for(int i = 1, x, y; i <= M; i++)
    {
        fin >> x >> y;

        G[x].push_back(i);
        G[y].push_back(i);
        V[i] = {x, y};
    }

    bool ok = Check();

    if(ok)
        Solve();
    else
        fout << "-1\n";

    fin.close();
    fout.close();

    return 0;
}