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

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

#define MAXN 110000
#define MAXM 510000

int N, M, used[MAXM];
vector<pair<int, int> > muchii;
vector<int> graph[MAXN], sol;

void doEuler (int nod) {
    for (int i = 0; i < graph[nod].size(); ++i) {
        int muchie = graph[nod][i];

        if (!used[muchie]) {
            int vecin = muchii[muchie].first + muchii[muchie].second - nod;

            used[muchie] = 1;

            doEuler(vecin);
        }
    }
    sol.push_back(nod);
}

bool avemSol () {
    for (int i = 1; i <= N; ++i)
        if (graph[i].size() % 2 != 0)
            return 0;
    return 1;
}

int main() {
    fin >> N >> M;

    for (int i = 1; i <= M; ++i) {
        int x, y;
        fin >> x >> y;

        muchii.push_back(make_pair(x, y));
        graph[x].push_back(muchii.size() - 1);
        graph[y].push_back(muchii.size() - 1);
    }

    doEuler(1);

    if (!avemSol()) {
        fout << -1;
        return 0;
    }

    for(int i = 0; i < sol.size(); ++i)
        fout << sol[i] << " ";

    return 0;
}