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

using namespace std;

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

int i, n, m, x, y;

vector < int > v[NMAX], ans;
stack < int > st;

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

    while (!st.empty())
    {
        int curr = st.top();

        while (v[curr].size())
        {
            int next = v[curr].back();
            v[curr].pop_back();
            v[next].erase(find(v[next].begin(), v[next].end(), curr));
            st.push(next);
            curr = next;
        }

        ans.push_back(st.top());
        st.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() == 0 || v[i].size() % 2 == 1)
    {
        g << -1;
        return 0;
    }

    euler(1);

    for (auto & it : ans)
        g << it << " ";
    return 0;
}