#include <fstream>
#include <vector>
#include <stack>
#include <queue>
#include <algorithm>

using namespace std;

fstream f("ciclueuler.in", ios::in);
fstream g("ciclueuler.out",ios::out);

const int nmax = 100010;

vector <int> a[nmax];
queue <int> q;
stack <int> s;

int n, m, i, x, y, grad[nmax], sol[nmax], viz[nmax], imposibil, nrs, nc, v;

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

void verifica()
{
    for (i = 1; i <= n; i++) if (grad[i] % 2 == 1) {
                                                    imposibil = 1;
                                                    return;
    }
    /*q.push(1);
    viz[1] = 1;
    while (!q.empty())
    {
        nc = q.front(); q.pop();
        for (vector <int>::iterator it = a[nc].begin(); it != a[nc].end(); ++it) if (!viz[*it]) {
                                                                                                viz[*it] = 1;
                                                                                                q.push(*it);
                                                                                                }
    }
    for (i = 1; i <= n; i++) if (!viz[i]) {
                                            imposibil = 1;
                                            return;
                                            }*/
}
void rezolva()
{
    s.push(1);
    while (!s.empty())
    {
        nc = s.top();
        if (a[nc].size())
        {
            v = a[nc].back();
            s.push(v);
            a[nc].pop_back();
            a[v].erase(find(a[v].begin(), a[v].end(), nc));
        }
        else
        {
            nrs++;
            sol[nrs] = nc;
            s.pop();
            if (nrs == m) return;
        }
    }
}

int main()
{
    citire();
    verifica();
    if (imposibil) g << "-1";
    else
    {
        rezolva();
        for (i = 1; i <= nrs; i++) g << sol[i] << " ";
    }
    return 0;
}