#include <fstream>
#include <vector>
using namespace std;

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

vector < pair <int, int> > v[500000];
bool viz[500010];
vector<int> cycle;
int n, m;

int ult = -1;

int st[500010];

void euler()
{
    st[++ult] = 1;
    while(ult != -1)
    {
        int nod = st[ult];
        if(!v[nod].empty())
        {
            int u = v[nod].back().first;
            int muchie = v[nod].back().second;
            v[nod].pop_back();
            if(!viz[muchie])
            {
                viz[muchie] = 1;
                st[++ult] = u;
            }
        }
        else
        {
            ult--;
        cycle.push_back(nod);
        }
    }

}

int main()
{
    fin >> n >> m;
    for(int i = 1; i <= m; i++)
    {
        int x, y;
        fin >> x >> y;
        v[x].push_back({y, i});
        v[y].push_back({x, i});
    }
    bool ex = true;
    for(int i = 1; i <= n && ex; i++)
    {
        if(v[i].size() % 2 != 0)
        {
            ex = false;
        }
    }
    if(!ex)
    {
        fout << -1;
    }
    else
    {
        euler();
        for(int i = cycle.size() - 1; i >= 0; i--)
        {
            fout << cycle[i] << ' ';
        }
    }
}