#include <bits/stdc++.h>
using namespace std;

ifstream fin("ciclueuler.in");
ofstream fout("ciclueuler.out");

int n, m;
int st[500005], dr[500005], poz[100005], e[500005];
vector<int> L[100005];
bitset<500005> viz;

bool Toate_Pare()
{
    for(int i = 1; i <= n; i++)
        if(L[i].size() % 2 == 1) return false;
    return true;
}
void DFS(int nod)
{
    while (poz[nod] < L[nod].size())
    {
        int k = L[nod][poz[nod]++];
        if (viz[k] == 0)
        {
            viz[k] = true;
            DFS(st[k] + dr[k] - nod);
        }
    }
    e[++m] = nod;
}

int main()
{
    int i;
    fin >> n >> m;
    for (i = 1; i <= m; i++)
    {
        fin >> st[i] >> dr[i];
        L[st[i]].push_back(i);
        L[dr[i]].push_back(i);
    }
    if (Toate_Pare() == false)
    {
        fout << -1;
        return 0;
    }

    m = 0;
    DFS(1);
    for (i = 1; i < m; i++)
        fout << e[i] << " ";
    return 0;
}