#include <iostream>
#include <fstream>
#include <vector>
#include <limits.h>

using namespace std;

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

const int N = 100005;
const int M = 500005;

// <destinatie, identificator muchie>
vector<pair<int, int>> g[N];
vector<int> ord;
bool viz[M];
int n, m;

void dfs(int nod)
{
    for (auto y : g[nod])
    {
        int dest = y.first;
        int id = y.second;
        if (!viz[id])
        {
            viz[id] = true;
            dfs(dest);
        }
    }

    ord.push_back(nod);
}

int main()
{
    fin >> n >> m;
    for (int i = 0; i < m; i++)
    {
        int x, y;
        fin >> x >> y;
        g[x].push_back({ y, i });
        g[y].push_back({ x, i });
    }

    // verificare
    for (int i = 1; i <= n; i++)
        if (g[i].size() % 2)
        {
            fout << -1;
            return 0;
        }

    dfs(1);

    ord.pop_back();
    for (int x : ord)
        fout << x << ' ';

    return 0;
}