# include <fstream>
# include <algorithm>
# include <vector>
# define NR 100005
using namespace std;
ifstream f("ciclueuler.in");
ofstream g("ciclueuler.out");
vector <int> v[NR], st;
int i,j,n,m,x,y;
int grad[NR], ap[NR];

void DFS (int k) {
    ap[k]=1;
    for (int i=0; i<v[k].size(); ++i)
        if (! ap[v[k][i]]) DFS (v[k][i]);
}
void euler (int k) {
    st.push_back(k);
    while (st.size()) {
        k=st.back();
        if (v[k].size()) {
            int y=v[k].back(); v[k].pop_back();
            st.push_back(y);

            v[y].erase (find(v[y].begin(), v[y].end(), k));
        }
        else {
            g<<k<<" ";
            st.pop_back();
        }
    }
}
int main ()
{
    f>>n>>m;
    for (i=1; i<=m; ++i) {
        f>>x>>y;
        v[x].push_back(y); ++grad[x];
        v[y].push_back(x); ++grad[y];
    }

    DFS (1);
    for (i=1; i<=n; ++i)
        if (grad[i]%2==1 || ap[i]==0) {
            g<<"-1\n";
            return 0;
        }

    euler (1);
    g<<"\n";

    return 0;
}