#include <fstream>
#include <vector>
#include <bitset>
#include <stack>
using namespace std;
const int NMAX = 100001,
          MMAX = 500001;

struct muchie
{
    int nod,
        nrm;

    muchie(int xx = 0, int nn = 0): nod(xx), nrm(nn) {}
};

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

int n, m;

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(muchie(y, i));
        G[y].push_back(muchie(x, i));
    }
}

void Euler()
{
    int x;
    muchie mm;
    S.push(1);
    while(!S.empty())
    {
        x = S.top();
        if(G[x].size() > 0)
        {
            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()
{
    bool ok = 1;
    citire();
    for(int i = 1; i <= n && ok; i++)
        if(G[i].size() & 1)
            ok = 0;
    if(ok)
    {
        Euler();
        for(int i = L.size() - 1; i >= 1; i--)
            g << L[i] << ' ';
    }
    else
        g << "-1\n";
    f.close();
    g.close();
    return 0;
}