#include <fstream>
#include <vector>
using namespace std;
ifstream f("ciclueuler.in");
ofstream g("ciclueuler.out");
struct data{
    int edge;
    bool used;
};
vector <data> v[100001];
int st[500001];
int main()
{
    data z;
    z.used=0;
    int n,m,i,ok,x,y,vf,act;
    f>>n>>m;
    for(i=1;i<=m;i++)
    {
        f>>x>>y;
        z.edge=y;
        v[x].push_back(z);
        z.edge=x;
        v[y].push_back(z);
    }
    ok=0;
    for(i=1;i<=n;i++)
    {
        if(v[x].size()%2==1)
            ok++;
    }
    if(ok!=0)
    {
        g<<-1<<'\n';
        return 0;
    }
    vf=1;
    st[vf]=1;
    while(vf>0)
    {
        act=st[vf];
        for(i=0;i<v[act].size();i++)
            if(v[act][i].used==0)
                break;
        if(i<v[act].size())
        {
            st[++vf]=v[act][i].edge;
            v[act][i].used=1;
            i=-1;
            do{
                i++;
                while(v[st[vf]][i].edge!=act)
                    i++;
            }while(v[st[vf]][i].used!=0);
            v[st[vf]][i].used=1;
        }
        else
        {
            g<<act<<' ';
            vf--;
        }
    }
    return 0;
}