#include <fstream>
#define M 500002
#define N 100002
#include <vector>

using namespace std;
ifstream f("ciclueuler.in");
ofstream g("ciclueuler.out");

int n,m,v[M],nr;
bool viz[M];
struct bla
{
    int ve,ord;
};
vector <bla> graph[N];

void euler(int nod)
{
    for(int i=0;i<graph[nod].size();++i)
    {
        int vee=graph[nod][i].ve;
        int mu=graph[nod][i].ord;
        if(!viz[mu])
            viz[mu]=1,euler(vee);
    }
    v[++nr]=nod;
}
int main()
{
    f>>n>>m;
    int x,y;
    for(int i=1;i<=m;++i)
    {
        f>>x>>y;
        graph[x].push_back({y,i});
        graph[y].push_back({x,i});
    }
    for(int i=1;i<=n;++i)
        if(graph[i].size()%2!=0)
        {
            g<<-1<<'\n';
            f.close();
            g.close();
            return 0;
        }
    euler(1);
    for(int i=1;i<nr;++i) g<<v[i]<<' ';
    f.close();
    g.close();
    return 0;
}