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


typedef std::vector< std::pair<int, int> >::iterator iter;


const int MAXN = 100005;
const int MAXM = 500005;
std::ifstream f("ciclueuler.in");
std::ofstream g("ciclueuler.out");
std::vector< std::pair<int, int> > G[MAXN]; int n, m;
std::bitset<MAXM> viz;
std::vector<int> sol;


bool is_euler()
{
    for (int i = 1; i <= n; i++) {
        if (G[i].size() % 2 != 0) {
            return false;
        }
    }
    return true;
}


void euler(int node)
{
    for (iter it = G[node].begin(); it != G[node].end(); it++) {
        if (!viz[it->second]) {
            viz[it->second] = true;
            euler(it->first);
        }
    }
    sol.push_back(node);
}


int main()
{
    f >> n >> m;
    for (int i = 1, x, y; i <= m; i++) {
        f >> x >> y;
        G[x].push_back(std::make_pair(y, i));
        G[y].push_back(std::make_pair(x, i));
    }


    if (!is_euler()) {
        g << -1 << '\n';
        f.close();
        g.close();
        return 0;
    }


    euler(1);

    for (int i = 1; i < sol.size(); i++) {
        g << sol[i] << ' ';
    }
    g << '\n';


    f.close();
    g.close();
    return 0;
}