#include <stdio.h>
#include <vector>
#include <deque>
#include <bitset>

using namespace std;
FILE* f, * g;
vector <pair <int, int> > nod[100002];
deque <int> q;
bitset <500008> viz;
int n, m;
void eulerian(int no)
{
    int muchie, vecin;
    while (nod[no].size())///mai are vecini
    {
        muchie = nod[no].back().second;///ordinul muchiei
        vecin = nod[no].back().first;
        nod[no].pop_back();///eliminam vecinul
        if (!viz[muchie])///nu am mai trecut prin muchia asta
            viz[muchie] = 1, eulerian(vecin);///mergem la urmatorul nod
    }
    q.push_back(no);///daca din nodul no nu mai putem merge in niciun alt nod, il introducem in coada finala
}

int main()
{
    int x, y;
    f = fopen("ciclueuler.in", "r");
    g = fopen("ciclueuler.out", "w");
    fscanf(f, "%d %d", &n, &m);
    for (int i = 1;i <= m;++i)
    {
        fscanf(f, "%d %d", &x, &y);
        nod[x].push_back({ y,i });///nodul x are ca si vecin nodul y si muchia dintre ele este de ordinul i;
        nod[y].push_back({ x,i });///idem
    }
    for (int i = 1;i <= n;++i)
        if (nod[i].size() % 2)///nodul i nu are grad par, deci nu admite ciclu Eulerian
        {
            fprintf(g, "-1\n");
            return 0;
        }
    eulerian(1);
    q.pop_back();
    while (!q.empty())
    {
        int x = q.front();
        fprintf(g, "%d ", x);
        q.pop_front();
    }
    fclose(f);
    fclose(g);
    return 0;
}