#include <fstream>
#include <vector>
#include <deque>

using namespace std;

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

int n, m;
bool muchii[500001];
struct vecin
{
    int nod;
    int muchie;

};


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

deque <int> c;
void BFS(int nod)
{
    int i;
    c.push_back(nod);
    v[nod] = true;
    while(!c.empty())
    {
        nod = c.front();
        c.pop_front();
        for( i = 0; i < lv[nod].size(); i++)
            if(!v[lv[nod][i].nod])
            {
                v[lv[nod][i].nod]=true;
                c.push_back(lv[nod][i].nod);
            }
    }
}

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

void euler(int nod)
{
    while(!lv[nod].empty())
    {
        int aux,i;

        i=lv[nod].size();
        while(i && muchii[lv[nod][i-1].muchie] == true)
            {
                i--;
                lv[nod].pop_back();
            }

        if(i)
        {
            muchii[lv[nod][i-1].muchie] = true;
            aux = lv[nod][i-1].nod;
            lv[nod].pop_back();
            c.push_back(nod);
            nod=aux;
        }
    }

}

void rezolvare()
{
    int x;

    x = 1;
    do
    {
        euler(x);
        x = c.back();
        c.pop_back();
        fout<< x <<" ";


    }
    while(!c.empty());
}

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

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

        aux.nod = y;
        lv[x].push_back(aux);
    }


    if(check())
           rezolvare();

        else fout << -1;

    return 0;
}