#include <iostream>
#include <fstream>
#include <list>
using namespace std;
ifstream ka("ciclueuler.in");
ofstream ki("ciclueuler.out");
const int N_MAX = 100000;
const int M_MAX = 500000;

struct muchie
{
    int index, id;
};

list <muchie> graf[N_MAX + 1];
int stiva[M_MAX + 1];

bool folosita[M_MAX + 1];
int grad[N_MAX + 1];

int n, m, a, b;

void cauta(int unde, int ce)
{
    bool gasit = false;
    for(list<muchie>::iterator it = graf[unde].begin(); it != graf[unde].end() && !gasit; ++it)
        if(it->index == ce)
        {
            graf[unde].erase(it);
            gasit = true;
        }
}

int main()
{
    ka >> n >> m;
    for(int i = 1; i <= m; i++)
    {
        ka >> a >> b;
        grad[a]++;
        grad[b]++;
        muchie mm;
        mm.index = b;
        mm.id = i;
        graf[a].push_back(mm);
        mm.index = a;
        graf[b].push_back(mm);
    }
    bool eulerian = true;
    for(int i = 1; i <= n && eulerian; i++)
        if(grad[i] == 0 || grad[i] % 2 == 1)
            eulerian = false;
    if(!eulerian)
        ki << -1;
    else
    {
        stiva[++stiva[0]] = 1;
        while(stiva[0])
        {
            int t = stiva[stiva[0]];
            bool gasita = false;
            for(list<muchie>::iterator it = graf[t].begin(); it != graf[t].end() && !gasita; ++it)
                if(!folosita[it->id])
                {
                    folosita[it->id] = true;
                    gasita = true;
                    stiva[++stiva[0]] = it->index;
                    cauta(it->index, t);
                    graf[t].erase(it);
                }
            if(!gasita)
            {
                if(stiva[0] != 1)
                    ki << t << " ";
                stiva[0]--;
            }
        }
    }
}