#include<stdio.h>
using namespace std;
const int N = 100005, M = 500005;
struct vect
{
    int x, y;
};
vect v[N];
int lst[N], urm[M], muchie[M], nr, c[M], nrc;
bool fol[M], grad[N];
void adauga (int x, int i)
{
    muchie[++nr] = i;
    urm[nr] = lst[x];
    lst[x] = nr;
}
int celalalt (int i, int x)
{
    if (v[i].x == x)
        return v[i].y;
    return v[i].x;
}
void euler (int x)
{
    int m, p, y;
    p = lst[x];
    while (p != 0)
    {
        m = muchie[p];
        if (fol[m] == false)
        {
            fol[m] = true;
            y = celalalt(m, x);
            euler (y);
        }
        p = urm[p];
    }
    c[++nrc] = x;
}
int main ()
{
    FILE *in, *out;
    in = fopen ("ciclueuler.in", "r");
    out = fopen ("ciclueuler.out", "w");
    int n, m, i;
    fscanf (in, "%d%d", &n, &m);
    for (i = 1; i <= m; i++)
    {
        fscanf (in, "%d%d", &v[i].x, &v[i].y);
        adauga (v[i].x, i);
        adauga (v[i].y, i);
        grad[v[i].x] = 1 - grad[v[i].x];
        grad[v[i].y] = 1 - grad[v[i].y];
    }
    euler(1);
    for (i = 1; i <= m; i++)
        if (grad[i])
        {
            fprintf (out, "-1");
            return 0;
        }
    for (i = 1; i <= m; i++)
        fprintf (out, "%d ", c[i]);
    return 0;
}