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

using namespace std;
const int NMAX = 100001,
          MMAX = 500001;

struct muchie
{
    int nod, nrm; /// nrm = numarul muchiei
};

int n, m;
vector<muchie> G[NMAX];
vector<int> L;
stack<int> S;
bitset<MMAX> elim;

ifstream f("ciclueuler.in");
ofstream g("ciclueuler.out");

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

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

int main()
{
    citire();
    for(int i = 1; i <= n; i++)
        if(G[i].size() & 1)
        {
            g << "-1";
            return 0;
        }
    //
    euler();
    L.pop_back();
    for(const auto &x : L)
        g << x << ' ';
    f.close();
    g.close();
    return 0;
}