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

using namespace std;

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

int i, j, n, m, x, y, l[5 * NMAX];
vector < int > v[NMAX], sol;
stack < int > q;

void euler(int node)
{
    q.push(node);

    while (!q.empty())
    {
        int current = q.top();
        l[current] = v[current].size();

        if (l[current])
        {
            int next = v[current].back();
            v[current].pop_back();
            v[next].erase(find(v[next].begin(), v[next].end(), current));
            q.push(next);
        }
        else
        {
            sol.push_back(current);
            q.pop();
        }
    }
}

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

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

    for (i = 1; i <= n; ++ i)
        if (v[i].size() & 1)
        {
            g << "-1";
            return 0;
        }

    for (i = 1; i <= n && !l[i]; ++ i)
        euler(i);

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

    return 0;
}