#include <iostream>
#include <fstream>
#include <vector>
#include <queue>
#include <stack>
#include <cstring>
#include <iterator>

using namespace std;

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

vector<pair<int, int > >x[100001];
vector<int> afis;
int viz[500001];


bool ver_ciclu(int n)
{
    for (int i = 1; i <= n; i++)
    {
        if (x[i].size() % 2 == 1)
            return 0;
    }
    return 1;
}

void rezolvare(int nod)
{
    while (!x[nod].empty())
    {
        auto nod_nou = x[nod].back();
        x[nod].pop_back();
        if (!viz[nod_nou.second])
        {
            viz[nod_nou.second] = 1;
            rezolvare(nod_nou.first);
        }
    }
    afis.push_back(nod);
}

int main()
{
    int n, m;
    f >> n >> m;
    for (int i = 1; i <= m; i++)
    {
        int a, b;
        f >> a >> b;
        x[a].push_back({ b,i });
        x[b].push_back({ a,i });
    }
    if (ver_ciclu(n) == 0)
        g << -1;
    else
    {
        rezolvare(1);
        afis.pop_back();
        vector <int>::iterator it;
        for (it = afis.begin(); it < afis.end(); it++)
        {
            g << *it << " ";
        }
    }
    return 0;
}