// Hierholzer's Algorithm
#include <fstream>
#include <vector>
#include <algorithm>
using namespace std;

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

vector<vector<pair<int, int>>> adj;
vector<bool> viz;
vector<int> ans;
int n, m, x, y;

bool IsEulerian()
{
    for (int i = 1; i <= n; ++i)
        if (adj[i].size() % 2)
            return false;
    return true;
}

void Dfs(int x)
{
    while (!adj[x].empty())
    {
        auto &[y, edge] = adj[x].back();
        adj[x].pop_back();
        if (!viz[edge])
        {
            viz[edge] = true;
            Dfs(y);
        }
    }
    ans.push_back(x);
}

int main()
{
    fin >> n >> m;
    adj.resize(n + 1);
    viz.resize(m + 1);
    for(int i = 1; i <= m; ++i)
    {
        fin >> x >> y;
        adj[x].push_back({y, i});
        adj[y].push_back({x, i});
    }
    
    if (IsEulerian())
    {
        Dfs(1);
        //reverse(ans.begin(), ans.end());
        for(size_t i = 0; i < ans.size() - 1; ++i)
            fout << ans[i] << " ";
    }
    else
       fout << "-1";
    return 0;
}