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

using namespace std;

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

int N, M;
vector<pair<int, int> > V[100001];
stack<int> ST;
bool instack[100001], used[500002];

int is_euler(int nod)
{
    ST.push(nod);
    instack[nod] = true;

    while (!ST.empty())
    {
        int now = ST.top();
        ST.pop();
        for (vector<pair<int, int> >::iterator it = V[now].begin(); it != V[now].end(); ++it)
        {
            if (!instack[it->first])
            {
                ST.push(it->first);
                instack[it->first] = true;
            }
        }
    }

    int ok = 1;
    for (int i = 1; i <= N; ++i)
    {
        if (V[i].size() % 2 == 1 || !instack[i])
        {
            ok = 0;
            break;
        }
    }

    return ok;
}

void solve_euler(int nod)
{
    ST.push(nod);

    while (!ST.empty())
    {
        int now = ST.top();

        bool ok = true;
        while (V[now].size() > 0)
        {
            pair<int, int> neighbour = V[now].back();
            V[now].pop_back();

            if (!used[neighbour.second])
            {
                used[neighbour.second] = true;
                ST.push(neighbour.first);
                ok = false;
                break;
            }
        }
        if (ok)
        {
            fout << now << ' ';
            ST.pop();
        }
    }
}

int main()
{
    fin >> N >> M;
    for (int i = 1, nod1, nod2; i <= M; ++i)
    {
        fin >> nod1 >> nod2;
        V[nod1].push_back(make_pair(nod2, i));
        V[nod2].push_back(make_pair(nod1, i));
    }

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

    solve_euler(1);

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