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

int N, M, X[500002], Y[500002], x, y, dim, sol[500002];
vector < int > G[100005];
bitset < 100005 > viz;

inline void euler(int nod)
{
    viz[nod]=1;
    vector <int>::iterator it=G[nod].begin();
    for (; it!=G[nod].end(); ++it)
        if (!viz[*it])
            viz[*it]=1, euler(X[*it]+Y[*it]-nod);
    sol[++dim]=nod;
}

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

    for (int i=1; i<=N; ++i)
        if (G[i].size()%2) { g<<-1<<'\n'; return 0; }

    euler(1);
    for (int i=1; i<=dim; ++i)
        g<<sol[i]<<' ';

    return 0;
}