#include <fstream>
#include <algorithm>
#include <vector>

using namespace std;

int N, M;
int E1[500002], E2[500002];
bool nok[500002];
int wh[100002];
vector<int> V[100002], result;
int ST[1000002];

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

    fin >> N >> M;
    for (int i = 1; i <= M; ++i)
    {
        fin >> E1[i] >> E2[i];
        V[E1[i]].push_back(i);
        V[E2[i]].push_back(i);
    }

    bool ok = true;
    for (int i = 1; i <= N; ++i)
        if (V[i].size() % 2 == 1)
        {
            ok = false;
            break;
        }

    if (!ok)
    {
        fout << -1 << '\n';
        fin.close();
        fout.close();
        return 0;
    }

    ST[++ST[0]] = 1;
    while (ST[0])
    {
        int x = ST[ST[0]], sznow = ST[0];
        for (int i = wh[x]; i < int(V[x].size()); ++i)
            if (!nok[V[x][i]])
            {
                int enow = V[x][i];

                int nod;
                if (E1[enow] == x) nod = E2[enow];
                else               nod = E1[enow];

                nok[enow] = true;
                ST[++ST[0]] = nod;

                ++wh[x];
                break;
            }
        if (ST[0] == sznow)
        {
            --ST[0];
            result.push_back(x);
        }
    }

    for (int i = 0; i < int(result.size()); ++i)
        fout << result[i] << ' ';
    fout << '\n';

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