#include <fstream>
#include <vector>
#include <utility>
 
using namespace std;
 
std::ifstream f("ciclueuler.in");
std::ofstream g("ciclueuler.out");
int N, M, nodStart;
vector<vector< pair<int, pair<bool, int>> >> Adiacenta;  // {nod vecin, {muchie de intoarcere?, indexul muchiei in lista lui nod_vecin}}
bool vizitat[100009];
vector<int> Solutie;
 
 
void DFS(int nodCurent, int nodTata)
{
    vizitat[nodCurent] = true;
    for (auto& vecin : Adiacenta[nodCurent])
    {
        if (!vizitat[vecin.first])
            DFS(vecin.first, nodCurent);
        else if (vecin.first != nodTata)
            vecin.second.first = 1;
    }
}
 
void Fleury()
{
    Solutie.reserve(M);
    int nodCurent = nodStart;
 
    for (;;)
    {
        Solutie.push_back(nodCurent);
 
        int nodUrmator = 0;
        int idx;
        for (size_t i = 0; i < Adiacenta[nodCurent].size(); ++i)
        {
            if (Adiacenta[nodCurent][i].first != 0)
            {
                idx = i;
                nodUrmator = Adiacenta[nodCurent][i].first;
                if (Adiacenta[nodCurent][i].second.first)
                    break;
            }
        }
 
        if (nodUrmator)
        {
            Adiacenta[nodCurent][idx].first = 0;
            idx = Adiacenta[nodCurent][idx].second.second;
            Adiacenta[nodUrmator][idx].first = 0;
 
            nodCurent = nodUrmator;
        }
        else
            break;
    }
 
    Solutie.pop_back();
}
 
int main()
{
    f >> N >> M;
    Adiacenta.resize(N + 1);
    for (int x, y, i = 0; i < M; ++i)
    {
        f >> x >> y;
        nodStart = x;
        if (x != y)
        {
            Adiacenta[x].push_back({y, {0, (int)Adiacenta[y].size()}});
            Adiacenta[y].push_back({x, {0, (int)Adiacenta[x].size() - 1}});
        }
        else
        {
            Adiacenta[x].push_back({y, {0, (int)Adiacenta[y].size() + 1}});
            Adiacenta[y].push_back({x, {0, (int)Adiacenta[x].size() - 1}});
        }
    }
    DFS(nodStart, 0);
    Fleury();
 
    if (Solutie.size() != M)
        g << -1;
    else
        for (auto nod : Solutie)
            g << nod << ' ';
 
    return 0;
}