#include <bits/stdc++.h>

using namespace std;

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

const int N = 500010;

vector<pair<int, int>> adj[N];
int n, m, st, dr;
int f[N], v[N];

int main()
{
    fin >> n >> m;
    for (int i = 1; i <= m; i++)
    {
        int x, y;
        fin >> x >> y;
        adj[x].push_back(make_pair(y, i));
        adj[y].push_back(make_pair(x, i));
    }

    for (int i = 1; i <= n; i++)
    {
        if (adj[i].size() % 2 == 1)
        {
            fout << -1;
            return 0;
        }
    }

    deque<int> d = {};

    d.push_front(1);

    while (!d.empty())
    {
        int nod = d.front();

        if (adj[nod].size() != 0)
        {
            int x = adj[nod][adj[nod].size() - 1].second;
            if (f[x] == 0)
            {
                f[x] = 1;
                d.push_front(adj[nod][adj[nod].size() - 1].first);
            }
            adj[nod].pop_back();
        }
        else
        {
            v[++st] = nod;
            d.pop_front();
        }
    }
    for (int i = 1; i <= st; i++)
        fout << v[i] << " ";
}