#include <bits/stdc++.h>

using namespace std;

const int Nmax = 100005;
const int Mmax = 500005;

vector < vector <int> > graf;
int n, m, grad[Mmax];
vector <int> sol;
bitset <Nmax> viz;

void euler(int start)
{
    vector <int> stiva;
    int nod, b;
    stiva.clear();
    stiva.push_back(start);
    while (!stiva.empty())
    {
        nod = stiva.back();
        if (graf[nod].empty())
        {
            stiva.pop_back();
            sol.push_back(nod);
            continue;
        }
        b = graf[nod].back();
        graf[nod].pop_back();
        stiva.push_back(b);
        for (vector <int>::iterator it = graf[b].begin(); it != graf[b].end(); it++)
        if (*it == nod) {graf[b].erase(it); break;}
    }
}

void dfs(int nod)
{
    viz[nod] = true;
    for (const auto &it : graf[nod])
        if (!viz[it])
        dfs(it);
}

int main()
{
    freopen("ciclueuler.in", "r", stdin);
    freopen("ciclueuler.out", "w", stdout);
    scanf("%d %d", &n, &m);
    graf.resize(n + 2);
    for (int i = 1, a, b; i <= m; i++)
    {
        scanf("%d %d", &a, &b);
        graf[a].push_back(b);
        graf[b].push_back(a);
        grad[a]++;
        grad[b]++;
    }
    dfs(1);
    for (int i = 1; i <= n; i++)
        if (!viz[i] || (grad[i] & 1))
        {
            printf("-1");
            return 0;
        }
    euler(1);
    sol.pop_back();
    for (const auto &it : sol)
        printf("%d ", it);
    return 0;
}