#include <fstream>
#include <algorithm>
#include <vector>
#define NMAX 100005

using namespace std;

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

int i, n, m, j, x, y;
vector < int > v[NMAX], sol;
bool used[5 * NMAX], ok = 1;

void euler(int node)
{
    while (v[node].size())
    {
        int current = v[node].back();
        v[node].pop_back();
        v[current].erase(find(v[current].begin(), v[current].end(), node));
        euler(current);
    }
    sol.push_back(node);
}

int main()
{
    f >> n >> m;

    for (i = 1; i <= n; ++ i)
    {
        f >> x >> y;
        v[x].push_back(y);
        v[y].push_back(x);
    }

    euler(1);

    for (i = 1; i <= n; ++ i)
        if (! v[i].empty())
        {
            ok = 0;
            break;
        }

    if (ok)
        for (vector < int > :: iterator it = sol.begin(); it != sol.end(); ++ it)
            g << *it << " ";
        else
            g << "-1";

    return 0;
}