#include <fstream>
#include <vector>
#include <stack>
#define NMAX 100002
#define MMAX 500002

using namespace std;
ifstream fin("ciclueuler.in");
ofstream fout("ciclueuler.out");
int n, m;
vector<int> sol, LA[NMAX];
stack<int> S;
struct muchie
{
    int x, y;
    bool uz;
};
muchie LM[MMAX];
void citire();
void ciclueuler();
void afisare();
bool ok();

int main()
{
    citire();
    if (!ok()) fout<<-1;
    else
    {ciclueuler();
    afisare();}
    return 0;
}
void citire()
{
    int i, x, y;
    fin>>n>>m;
    for (i=1; i<=m; i++)
    {
        fin>>x>>y;
        LM[i].x=x;
        LM[i].y=y;
        LA[x].push_back(i);
        LA[y].push_back(i);
    }
}
void ciclueuler()
{
    int urm, x;
    S.push(1);
    while (!S.empty())
    {
        x=S.top();
        if (LA[x].size()==0)
        {
            sol.push_back(x);
            S.pop();
        }
        else
        {
            urm=LA[x].back();
            LA[x].pop_back();
            if (LM[urm].uz==0)
            {
                LM[urm].uz=1;
                if (x==LM[urm].x)
                    S.push(LM[urm].y);
                else S.push(LM[urm].x);
            }
        }
    }
}
void afisare()
{
    int i;
    for (i=0; i<sol.size()-1; i++)
        fout<<sol[i]<<" ";
}
bool ok()
{
    int i;
    for (i=1; i<=n; i++)
        if (LA[i].size()%2) return 0;
    return 1;
}