#include <stdio.h>
#include <vector>
#include <list>
using namespace std;
#define N 800000
struct Nod {
    int x;
    Nod *next;
};
int n, m;
int que[N];
list <int> a[N];
int lista[N];
int gr[N];
int stack[N];
int viz[N];

void find_tour(int s) {
    int top = 1;
    int it;
    stack[top] = s;
    while (top > 0) {
      while (a[stack[top]].size() != 0) {
            int n = a[stack[top]].front();
            a[stack[top]].pop_front();
            list<int>::iterator it2;
            for(it2 = a[n].begin(); it2 != a[n].end(); it2++)
             if (*it2 == stack[top]) {a[n].erase(it2); break;}
            stack[++top] = n;
        }
        lista[++lista[0]] = stack[top];
        top--;
     }
}
int bf(int s) {
    int st = 1, dr = 1;
    list<int>::iterator it;
    que[1] = s;
    viz[s] = 1;
    while (st <= dr) {
        for(it = a[que[st]].begin(); it != a[que[st]].end(); it++)
         if (!viz[*it]) {
          que[++dr] = *it;
          viz[*it] = 1;
         }
        st++;
    }
}
int este_conex() {
    bf(1);
    for(int i = 1; i <= n; i++)
     if (viz[i] == 0) return 0;
    return 1;
}
int grad_par() {
    for(int i = 1; i <= n; i++)
     if (gr[i] % 2 != 0) return 0;
    return 1;
}
int main()
{
    freopen("ciclueuler.in","r",stdin);
    freopen("ciclueuler.out","w",stdout);
    scanf("%d %d",&n,&m);
    for(int i = 1; i <= m; i++) {
        int u,v;
        scanf("%d %d",&u,&v);
        gr[u]++;
        gr[v]++;
        a[u].push_back(v);
        a[v].push_back(u);
        /*insert(a[u], v);
        insert(a[v], u);*/
    }
    if (este_conex() && grad_par()) {
        find_tour(1);
        for(int i = 1; i < lista[0]; i++)
            printf("%d ",lista[i]);
        printf("\n");
    }
    else
     printf("-1\n");
    return 0;
}