#include<stdio.h>
using namespace std;
const int N = 100005,
          M = 500005;
int e[2 * M], urm[2 * M], lst[N], x[N], y[N], nr, folosit[N], ok = true, rc, viz[M], p, i2, c[M], pare[N];
int celalalt (int i, int x2)
{
    if (y[i] != x2)
        return y[i];
    return x[i];
}
void adauga (int i)
{
    e[++nr] = i;
    urm[nr] = lst[x[i]];
    lst[x[i]] = nr;
    e[++nr] = i;
    urm[nr] = lst[y[i]];
    lst[y[i]] = nr;
}
void euler (int x2)
{
    int y;
    p = lst[x2];
    while (p != 0)
    {
        i2 = e[p];
        y = celalalt (i2, x2);
        if (!folosit[i2])
        {
            folosit[i2] = true;
            euler(y);
        }
        p = urm[p];
    }
    c[++rc] = x2;
}
int main ()
{
    FILE *in, *out;
    in = fopen ("ciclueuler.in", "r");
    out = fopen ("ciclueuler.out", "w");
    int n, m;
    fscanf (in, "%d%d", &n, &m);
    int i;
    for (i = 1; i <= m; i++)
    {
        fscanf (in, "%d%d", &x[i], &y[i]);
        pare[x[i]]++;
        pare[y[i]]++;
        adauga(i);
    }
    euler(1);
    int ok2 = true;
    for (i = 1; i <= rc; i++)
        viz[c[i]] = true;
    for (i = 1; i <= n; i++)
    {
        if (viz[i] == 0)
            ok2 = false;
        if (pare[i] % 2 != 0)
            ok = false;
            }
    if (ok == true && ok2 == true)
        for (i = 1; i <= rc; i++)
            fprintf (out, "%d ", c[i]);
    else
        fprintf (out, "-1");
    return 0;
}