#include <bits/stdc++.h>
using namespace std;

struct elem
{
    int node, poz;
};

vector <elem> v[100001];

stack <int> st, sol;

bool viz[100001];

int lg[100001];

int n, m;

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

    f >> n >> m;

    for(int i = 1; i <= m; ++ i)
    {
        int x, y;

        f >> x >> y;

        v[x].push_back({y, i});
        v[y].push_back({x, i});
    }

    for(int i = 1; i <= n; ++ i)
        if(v[i].size() % 2 == 1)
        {
            g << "-1";
            return 0;
        }

    /*
    for(int i = 1; i <= n; ++ i)
        cout << i << " " << v[i].size() << "\n";
    */

    st.push(1);

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

        if(lg[node] < v[node].size())
        {
            int vecin = v[node][lg[node]].node;
            int poz = v[node][lg[node]].poz;

            lg[node] ++;

            if(viz[poz] == 0)
            {
                st.push(vecin);

                viz[poz] = 1;
            }
        }
        else
        {
            st.pop();
            sol.push(node);
        }
    }

    // afisarea stivei
    while(!sol.empty())
    {
        int node = sol.top();
        sol.pop();
        if(!sol.empty())
            g << node << " ";
    }
    return 0;
}