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

using namespace std;

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

int N, M;
vector <vector <int> > g;
vector <pair <int, int> > edges;
vector <bool> usedEdge;
vector <int> ciclu;

void readGraph() {
    fin >> N >> M;
    g.resize(N + 1);
    edges.resize(M + 1);
    usedEdge.resize(M + 1, false);

    int x, y;
    for (int i = 1; i <= M; ++i) {
        fin >> x >> y;
        edges[i] = {x, y};
        g[x].push_back(i);
        g[y].push_back(i);
    }
}

bool checkEuler() {
    for (auto x: g) {
        if (x.size() % 2 == 1)
            return 0;
    }
    return 1;
}

void generateCycle(int node) {
    int p;
    for (const int& edge: g[node]) {
        if (!usedEdge[edge]) {
            p = edges[edge].first;
            usedEdge[edge] = 1;
            if (p == node)
                p = edges[edge].second;
            generateCycle(p);
        }
    }
    ciclu.push_back(node);
}

int main()
{
    readGraph();
    if (checkEuler()) {
        generateCycle(1);
        ciclu.pop_back();
        for (auto& t: ciclu)
            fout << t << ' ';
    }
    else
        fout << -1;

    fin.close();
    fout.close();
    return 0;
}