#include <fstream>
#include <vector>
#define DMAX 100005
using namespace std;
ifstream fin ("test.in");
ofstream fout ("test.out");

void citire();
bool verifica();
void euler();
void sterge (int, int);

int n, m, grad[DMAX];
vector <int> G[DMAX], sol, coada;

int main()
{
    int i;
    
    citire();
    if (verifica())
    {
        euler();
        for (i=0; i<m; i++) fout<< sol[i]<<' ';
    }
    else fout<< "-1\n";
    
    fin.close();
    fout.close();
    return 0;
}

void euler()
{
    int nod=1, v;
    
    //coada.push_back(0);
    coada.push_back(nod);
    
    while (coada.size())
    {
        nod = coada.back();
        if (G[nod].size())
        {
            v=G[nod][0];
            G[nod].erase(G[nod].begin());
            
            sterge(v, nod);
            //nrc++;
            coada.push_back(v);
        }
        else
        {
            sol.push_back(coada.back());
            coada.erase(coada.end()-1);
            //nrc--;
        }
    }
}

void sterge(int lin, int val)
{
    vector <int> ::iterator it;
    
    for (it = G[lin].begin(); it != G[lin].end(); it++)
        if (*it == val)
        {
            G[lin].erase(it);
            return;
        }
}

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

bool verifica()
{
    for (int i=1; i<=n; i++)
        if (grad[i]%2)
            return 0;
    return 1;
}