#include <iostream>
#include <fstream>
#include <vector>

using namespace std;

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

int n, m;
vector<int> G[100001], R;
vector<pair<int, int>> M;
bool V[500001];

void Dfs(int x)
{
    for (int i : G[x])
    {
        if (!V[i])
        {
            V[i] = true;
            Dfs(M[i].first == x ? M[i].second : M[i].first);
        }
    }
    R.push_back(x);
}

int main()
{
    fin >> n >> m;
    for (int i = 0; i < m; ++i)
    {
        int x, y;
        fin >> x >> y;
        M.emplace_back(x, y);
        G[x].push_back(i);
        G[y].push_back(i);
    }
    for (int i = 1; i <= n; ++i)
    {
        if (G[i].size() == 0 || G[i].size() % 2 == 1)
        {
            fout << -1;
            return 0;
        }
    }
    Dfs(1);
    for (int i = 1; i < R.size(); ++i)
        fout << R[i] << " ";

    return 0;
}