#include <fstream>
#include <bitset>
#include <vector>

using namespace std;

const int NMAX = 1e5 + 1, MMAX = 5e5 + 1;

struct muchie
{
    int nod, nrm;
};

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

int n, m;

vector<muchie> G[NMAX];
vector<int> L;
bitset<MMAX> elim;

void citire()
{
    int x, y;
    fin >> n >> m;
    for(int i = 1; i <= m; ++i)
    {
        fin >> x >> y;
        G[x].push_back({y, i});
        G[y].push_back({x, i});
    }
}

void euler(int x)
{
    muchie mm;
    while(!G[x].empty())
    {
        mm = G[x].back();
        G[x].pop_back();
        if(!elim[mm.nrm])
        {
            elim[mm.nrm] = 1;
            euler(mm.nod);
        }
    }
    L.push_back(x);
}

int main()
{
    bool ok = 1;
    citire();
    for(int i = 1; i <= n; ++i)
        if(G[i].size() & 1)
        {
            ok = 0;
            break;
        }
    if(ok)
    {
        euler(1);
        L.pop_back();
        for(const auto& x : L) fout << x << ' ';
    }
    else fout << "-1";
    return 0;
}