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

using namespace std;

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

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

};


bool v[100001];
vector <vecin> lv[100001];
vector <int> st;
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( gr[i] % 2 ) return 0;
    BFS(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();
            }
        if(i && m2 < m-1)
        {


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

}

void rezolvare()
{
    while(!st.empty())
    {
        int x = st.back();
        st.pop_back();
        euler(x);
    }
}

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;
}