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

using namespace std;

ifstream f("ciclueuler.in");
ofstream g("ciclueuler.out");
const int MMAX = 500001, NMAX = 100001;
vector<pair<int, int>> muchii;
bitset<MMAX> viz;
vector<pair<int, int>> G[NMAX];///.first - nodul , .second - indicele muchiei
vector<int> path;

void DFS(int nod)
{
    while (!G[nod].empty())
    {
        auto vec = G[nod].back();
        G[nod].pop_back(); /// nu mai vreau sa merg pe muchia asta
        int nodVec = vec.first;
        int idxMuchie = vec.second;
        if (viz[idxMuchie])
        {
            continue;
        }
        viz[idxMuchie] = true;
        DFS(nodVec);
    }
    path.push_back(nod);
}

int main()
{
    int n, m;
    f >> n >> m;
    for (int i = 0; i < m; i++)
    {
        int x, y;
        f >> x >> y;
        muchii.emplace_back(x, y);
        G[x].emplace_back(y, i);
        G[y].emplace_back(x, i);
    }
    for (int i = 1; i <= n; i++)
    {
        if (G[i].size() & 1) /// ca sa existe un ciclu eulerian e nevoie ca toate nodurile sa aiba grad par
        {
            g << -1;
            return 0;
        }
    }
    DFS(1);
    path.pop_back();
    for (auto nod: path)
    {
        g << nod << ' ';
    }

    return 0;
}