#include<fstream>
#include<vector>
#include<algorithm>
#include<stack>
using namespace std;
ifstream cin ("ciclueuler.in");
ofstream cout ("ciclueuler.out");
struct ura{
    int nod, muchie;
};
int k, viz[500005], st[100005];
vector <ura> v[100005];
void euler (int nod)
{
    while (v[nod].size())
    {
        ura aux = v[nod].back();
        v[nod].pop_back();
        if (!viz[aux.muchie])
        {
            viz[aux.muchie] = 1;
            euler(aux.nod);
        }
    }
    st[++k] = nod;
}
int main ()
{
    int n, m, i;
    cin >> n >> m;
    for (i = 1; i <= m; i++)
    {
        int x, y;
        cin >> x >> y;
        v[x].push_back({y, i});
        v[y].push_back({x, i});
    }
    for (i = 1; i <= n; i++)
    {
        if (v[i].size() % 2)
        {
            cout << -1;
            return 0;
        }
    }
    k = 0;
    euler(1);
    for (i = 1; i < k; i++)
        cout << st[i] <<" ";
    return 0;
}