#include <iostream>
#include <fstream>
#include <vector>

using namespace std;

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

int n, m;
vector<vector<pair<int, int>>> adj_list;
vector<int> noduri;
vector<int> viz;
void euler(int nod_start){
    for(pair<int, int> v : adj_list[nod_start]){
        int muchie = v.second;
        if (!viz[muchie]) {
            viz[muchie] = 1;
            euler(v.first);
        }
    }
    noduri.push_back(nod_start);
}
int main()
{
    fin>>n>>m;
    adj_list.assign(n+1, {});
    viz.assign(m+1, 0);
    vector<int> grade(n+1, 0);

    for(int i=1; i<=m; i++){
        int x, y;
        fin>>x>>y;
        adj_list[x].push_back({y, i});
        adj_list[y].push_back({x, i});
        grade[x]+=1;
        grade[y]+=1;
    }
    for (auto grad : grade){
        if (grad % 2 == 1){
            fout<<-1;
            return 0;
        }
    }

    euler(1);
    noduri.pop_back();
    if (!(noduri.size() == m)){
        fout<<-1;
        return  0;
    }
    for (auto i : noduri){
        fout<<i<<" ";
    }

    return 0;
}