#include <fstream>
#include <vector>
using namespace std;
ifstream fin("ciclueuler.in");
ofstream fout("ciclueuler.out");
vector<pair <int, int> > nodes[100005];
int ciclu[500005], n, m, p, q, k;
bool viz[500005];
void euler(int nod)
{
    while (!nodes[nod].empty())
    {
        p = nodes[nod].back().second;
        q = nodes[nod].back().first;
        nodes[nod].pop_back();
        if (!viz[p])
        {
            viz[p] = 1;
            euler(q);
        }
    }
    ciclu[++k] = nod;
}
int main()
{

    fin >> n >> m;
    for (int i = 1; i <= m; ++i)
    {
        int x,y;
        fin >> x >> y;
        nodes[x].push_back({ y, i });
        nodes[y].push_back({ x, i });
    }
    int ok = 1;
    for (int i = 1; i <= n; i++)
        if (nodes[i].size() % 2 == 1)
        {
           fout << -1;
            ok = 0;
            break;
        }
        if(ok == 1)
        {
                euler(1);
    for (int i = 1; i < k; i++)
        fout << ciclu[i] << ' ';
        }

return 0;
}