#include <fstream>
#include <vector>
#include <queue>
#define lim 500004
#define f first
#define s second
using namespace std;
ifstream f("ciclueuler.in");
ofstream g("ciclueuler.out");
int n,m,u,v,viz[lim];
vector <pair <int,int> > G[lim];
queue <int> q;
void euler (int nod)
{
    for (auto vec:G[nod])
    {
        if (viz[vec.s]==0)
        {
            viz[vec.s]=1;
            euler(vec.f);
        }
    }
    q.push(nod);
}
int main()
{
    f>>n>>m;
    for (int i=1;i<=m;i++)
    {
        f>>u>>v;
        G[u].push_back({v,i});
        G[v].push_back({u,i});
    }
    for (int i=1;i<=n;i++)
        if (G[i].size()%2==1)
        {
            g<<-1;
            return 0;
        }
    euler(1);
    while (!q.empty())
    {
        g<<q.front()<<' ';
        q.pop();
    }
    f.close();
    g.close();
    return 0;
}