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

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

bool ok()
{
    for (int i=1; i<=N; ++i)
        if (G[i].size()%2) return 0;
    return 1;
}

void euler(int nod)
{
    st.push(nod);
    while (st.size())
    {
        int crt=st.top();
        if (G[crt].size())
        {
            int last=G[crt].back();
            st.push(last); G[crt].pop_back();
            G[last].erase( find(G[last].begin(), G[last].end(), crt) );
        }
        else st.pop(), sol.push_back(crt);
    }
}

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);
    }

    if (!ok()) { g<<-1<<'\n'; return 0; }

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