#include <fstream>
#include <vector>
#include <stack>
#include <algorithm>
using namespace std;
ifstream f("ciclueuler.in");
ofstream g("ciclueuler.out");

int N, M, x, y;
vector < int > G[100005], sol;
stack < int > st;

void df(int nod)
{
    int nou;
    if(G[nod].size())
    {
        nou=G[nod][0];
        G[nod].erase(G[nod].begin()); st.push(nou);
        G[nou].erase( find(G[nou].begin(), G[nou].end(), nod) );
        df(nou);
    }
}

void ciclu(int x)
{
    st.push(x);
    while (!st.empty())
    {
        int nod=st.top();
        /*if (G[nod].size())
        {
            int last=G[nod].back();
            G[nod].pop_back(); st.push(last);
            G[last].erase( find(G[last].begin(), G[last].end(), nod) );
        }*/
       // else
       df(nod);
       sol.push_back(nod), st.pop();
    }
}

int main()
{
    f>>N>>M;
    for (int i=1; i<=M; ++i)
        f>>x>>y, G[x].push_back(y), G[y].push_back(x);

    for (int i=1; i<=N; ++i)
        if (G[i].size()&1) { g<<-1<<'\n'; return 0; }

    ciclu(1);
    for (int i=0; i<(int)sol.size()-1; ++i)
        g<<sol[i]<<' ';
    g<<"alabalaportocala";
    return 0;
}