#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#define maxn 100001

struct list{ int v; struct list *next; } *G[maxn];
int N, D[maxn], Q[500000], top;
FILE *in, *out;

int eulerian();
int conex();
void erase(int a, int b);

int main ()
{
    int i, a, b;
    struct list *p;

    in = fopen ("ciclueuler.in", "r");
    fscanf (in, "%d %d", &N, &i);
    for (; i; --i)
    {
        fscanf (in, "%d %d", &a, &b);
        D[a]++, D[b]++;

        p = malloc (sizeof(struct list));
        p->v = b; p->next = G[a]; G[a] = p;

        p = malloc (sizeof(struct list));
        p->v = a; p->next = G[b]; G[b] = p;
    }
    fclose (in);

    out = fopen ("ciclueuler.out", "w");

    if (!eulerian())
        fprintf (out, "-1");
    else
        for (top = 0, Q[0] = 1; top >= 0;)
        {
            if ( D[ Q[top] ] == 0 )
            {
                fprintf(out, "%d ", Q[top]);
                top--;
            }
            else
                for (p = G[ Q[top] ]; p; p = p->next)
                {
                    D[ Q[top] ]--; D[p->v] --;
                    Q[++top] = p->v;
                    erase (Q[top-1], p->v);
                    break;
                }
        }

    fprintf(out, "\n");
    fclose (out);
    return 0;
}

void erase(int a, int b){
    struct list *p, *i;

    for (i = NULL, p = G[a]; p->v != b; i = p, p = p->next);
    if(i == NULL)
    {
        G[a] = p->next;
        free(p);
    }
    else
    {
        i->next = p->next;
        free(p);
    }

    for (i = NULL, p = G[b]; p->v != a; i = p, p = p->next);
    if(i == NULL)
    {
        G[b] = p->next;
        free(p);
    }
    else
    {
        i->next = p->next;
        free(p);
    }
}

int eulerian(){
    int i;

    for(i = 1; i <= N; ++i)
        if(D[i] % 2 == 1)
            return 0;
    return conex();
}

int conex(){
    char used[maxn];
    int l, r;
    struct list *p;

    memset(used, 0, sizeof(used));
    Q[0] = 1;
    used[1] = 1;

    for(l = r = 0; l <= r; ++l)
        for(p = G[ Q[l] ]; p; p = p->next)
            if(!used[p->v]){
                used[p->v] = 1;
                Q[++r] = p->v;
            }

    for(l = 1; l <= N; ++l)
        if(!used[l])
            return 0;
    return 1;
}