#include <fstream>
#include <vector>

using namespace std;

ifstream fin("ciclueuler.in");
ofstream fout("ciclueuler.out");

int n,m;
int gr[100001], marb[100001];
bool muchii[500001];
bool ma[500001];
int m2;
struct vecin
{
    int nod;
    int muchie;

};


bool v[100001];
vector <vecin> lv[100001];

void DFS(int nod)
{
    int i;

    v[nod] = true;

    for( i = 0; i < lv[nod].size(); i++ )
    {
        if( !v[ lv[nod][i].nod])
            {
                marb[nod]++;
                ma[lv[nod][i].muchie] = true;
                vecin aux;
                aux=lv[nod][marb[nod]-1];
                lv[nod][marb[nod]-1]=lv[nod][i];
                lv[nod][i]=aux;
                DFS( lv[nod][marb[nod]-1].nod);

            }
    }
}

bool check()
{
    int i;
    for( i = 1; i <= n; i++)
        if( gr[i] % 2 ) return 0;
    DFS(1);
    for( i = 1; i <= n; i++)
        if( v[i] == false ) return 0;
    return 1;
}

void euler(int nod)
{

        int aux,i;
        i=lv[nod].size();
        while(i && muchii[lv[nod][i-1].muchie] == true)
            {
                i--;
                lv[nod].pop_back();
            }
        while( i > marb[nod] && ma[lv[nod][i-1].muchie] == true)
            {
                marb[ nod ] ++;
                vecin aux;
                aux= lv[nod][marb[nod]-1];
                lv[nod][marb[nod]-1]=lv[nod][i-1];
                lv[nod][i-1]=aux;

            }
        if(i)
        {
            muchii[lv[nod][i-1].muchie] = true;
            aux=lv[nod][i-1].nod;
            fout << aux<<" ";
            m2++;
            lv[nod].pop_back();

            if(m2 < m) euler(aux);
        }
}

int main()
{
    fin >> n >> m;
    int i;

    for( i = 1; i <= m; i++)
    {
        int x, y;
        fin >> x >> y;
        gr[x]++;
        gr[y]++;
        vecin aux;
        aux.nod=x;
        aux.muchie=i;

        lv[y].push_back(aux);

        aux.nod=y;

        lv[x].push_back(aux);
    }


    if(check())
        {
            fout<< 1<<" ";
            euler(1);
        }
        else fout << -1;

    return 0;
}