#include <fstream>
#include <iostream>
#include <queue>
#include <set>
#include <vector>
 
using namespace std;
ifstream fin ("ciclueuler.in");
ofstream fout ("ciclueuler.out");
 
int f[500001], a[500001], b[500001], n, m;
 
vector <int> mc[500001];
vector <int> sol;
 
void euler(int nod)
{
    int nod2, muchie;
    
    while (mc[nod].size() != 0)
    {
        muchie = mc[nod].back();
        mc[nod].pop_back();
        
        if(f[muchie] == 0)
        {
            f[muchie] = 1;
        
        if(a[muchie] == nod)
            nod2 = b[muchie];
        else
            nod2 = a[muchie];
        euler(nod2);
        }
    }
    sol.push_back(nod);
}
 
int main()
{
    int i;
    fin >> n >> m;
    for (i = 1; i<= m; i++)
    {
        fin >> a[i] >> b[i];
        mc[a[i]].push_back(i);
        mc[b[i]].push_back(i);
    }
    
    for (i = 1; i<= n; i++)
        if(mc[i].size() % 2 == 1)
        {
            fout << "-1";
            return 0;
        }
    
    euler(1);
    
    for (i = 0; i< sol.size(); i++)
        fout << sol[i] << " ";
    
}