#include <fstream>
#include <vector>
#include <cstring>
using namespace std;

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

int n, m, grad[100001];
vector<int> adj[100001];
pair<int, int> M[500001];
bool b[500001];

void dfs(int nod)
{
    bool ok = true;

    while (adj[nod].size())
    {
        int edge = adj[nod].back();
        adj[nod].pop_back();
        if (!b[edge])
        {
            if (ok)
            {
                ok = false;
                fout << nod << ' ';
            }
            b[edge] = 1;
            if (M[edge].first != nod)
                dfs(M[edge].first);
            else
                dfs(M[edge].second);
        }
    }
}

int main()
{
    int x, y, cnt_impar = 0, start = 1;

    fin >> n >> m;
    for (int i = 0; i < m; i++)
    {
        fin >> x >> y;
        M[i] = make_pair(x, y);
        adj[x].push_back(i);
        if (x != y)
            adj[y].push_back(i);
        grad[x]++;
        grad[y]++;

    }

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

    dfs(1);

    return 0;
}