# include <iostream>
# include <fstream>
# include <vector>
# include <bitset>
using namespace std;

# define MAXN 100010
# define MAXM 500010
typedef vector< pair<int, int> >::iterator iter;

ifstream f("ciclueuler.in");
ofstream g("ciclueuler.out");

int n, m;
vector< pair<int, int> > G[MAXN];
bitset<MAXM> vizmuchie;
vector<int> sol;

void euler(int nod) {
    for (int i = 0; i < G[nod].size(); i++) {
        if (vizmuchie[G[nod][i].second] == false) {
            vizmuchie[G[nod][i].second] = true;
            euler(G[nod][i].first);
        }
    }
    sol.push_back(nod);
}

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

    euler(1);
    sol.pop_back();

    if (sol.size() == m) {
        for (int i = 0; i < sol.size(); i++) {
            g << sol[i] << ' ';
        }
    } else {
        g << '-1';
    }

    /*bool ok = true;
    for (int i = 1; i <= m; i++) {
        if (vizmuchie[i] == false) {
            ok = false;
        }
    }*/

    return 0;
}