#include <iostream>
#include <fstream>
#include <vector>
using namespace std;
ifstream f("ciclueuler.in");
ofstream g("ciclueuler.out");

int n, m;
vector <int> G[1000001];
vector <int> sol;
int a[500001], b[500001];
bool viz[500001];
int ok;

void citire()
{
    f >> n >> m;
    for(int i = 1; i <= m; i++)
    {
        f >> a[i] >> b[i];
        G[a[i]].push_back(i);
        G[b[i]].push_back(i);
    }
}

void euler(int poz)
{
    while(G[poz].size())
    {
        int x = G[poz].back(); ///muchia curenta
        G[poz].pop_back();

        if(viz[x] != 0)
            continue;

        viz[x] = 1;
        int vecin;
        if(a[x] == poz)
            vecin = b[x];
        else
            vecin = a[x];
        euler(vecin);
    }
    sol.push_back(poz);
}

int main()
{
    citire();
    //
    for(int i = 1; i <= n; i++)
    {
        if(G[i].size() % 2 == 1)
        {
            g << "-1";
            return 0;
        }
    }
    euler(1);
    for(int i = 0; i < sol.size(); i++)
        g << sol[i] << ' ';
    return 0;

}