#include <fstream>
#include <vector>
#define nmax 100010
#include <list>
using namespace std;
ifstream f("ciclueuler.in");
ofstream g("ciclueuler.out");
vector <int> v[nmax];
list <int> q;
struct muchie
{
    int st,dr,use;
} mu[5*nmax];
int viz[nmax],gr[nmax],ok,nr,n,m;

void euler(int i)
{
    int nod,vec,j,ind;
    q.push_back(i);
    while(!q.empty())
    {
        nod=q.front();
        if(v[nod].empty())
        {
            q.pop_front();
            if(nod!=i) g<<nod<<' ';
        }
        else
        {
            ind=v[nod].back();
            v[nod].pop_back();
            if(!mu[ind].use)
            {
                mu[ind].use=1;
                if(mu[ind].st==nod) vec=mu[ind].dr;
                else vec=mu[ind].st;
                q.push_front(vec);
            }
        }
    }
}
int main()
{
    int i,x,y;
    f>>n>>m;
    for(i=1; i<=m; i++)
    {
        f>> mu[i].st>>mu[i].dr;
        v[mu[i].st].push_back(i);
        v[mu[i].dr].push_back(i);
        gr[mu[i].st]++;
        gr[mu[i].dr]++;
    }
    ok=1;
    for(i=1; i<=n&&ok; i++)
        if(gr[i]%2) ok=0;
    if(ok) {g<<1<<' ';euler(1);}
    else g<<-1;
    return 0;
}