#include <fstream>
#include <stack>
#include<vector>
#define NMAX 100002
#define MMAX 500002
using namespace std;
ifstream fin("ciclueuler.in");
ofstream fout("ciclueuler.out");
struct varf
{
    int x,nr;
}; //x -vf adiacent ; nr-nr muchiei corespunzatoare
vector<varf>G[NMAX];
int n,m,d[NMAX];
bool uz[MMAX]; //1-utilizata pe ciclu
vector<int>sol;
bool eulerian;
void citire();
void euler(int start);
int main()
{
    int i;
    citire();
    //returneaza 0 daca nu toate gr sunt pare
    //daca toate sunt pare returneaza indicele unui vf care nu e izolat
    for(i=1; i<=n; i++)
    {
        if(d[i]%2)
        {
            fout<<-1<<'\n';
            return 0;
        }
    }
    euler(1);
    sol.pop_back();
    for(i=0; i<sol.size(); i++)
    {
        fout<<sol[i]<<' ';
    }

}
void citire()
{
    int i,x,y;
    varf vf;
    fin>>n>>m;
    for(i=1; i<=m; i++)
    {
        fin>>x>>y;
        //y intra in lista de adi a lui x
        vf.x=y;
        vf.nr=i;
        G[x].push_back(vf);
        //x intra in lista de adi a lui y
        vf.x=x;
        vf.nr=i;
        G[y].push_back(vf);
        d[x]++;
        d[y]++;
    }
}

void euler(int start)
{
    while(!G[start].empty())
    {
        varf a=G[start].back();
        G[start].pop_back();
            if(!uz[a.nr])
            {
                uz[a.nr]=1;
                euler(a.x);
            }
    }
    sol.push_back(start);
}