#include <bits/stdc++.h>

using namespace std;

ifstream fin("ciclueuler.in");
ofstream fout("ciclueuler.out");

int lg[100005];
bool viz[500005];

struct elem
{
    int node, poz;
};

vector <elem> v[100005];

stack <int> st, sol;

int n, m;

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

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

        fin >> 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)
    {
        fout << -1;
        return 0;
    }

    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);
        }
    }

    while(!sol.empty())
    {
        int node = sol.top();
        sol.pop();
        if(!sol.empty())
        fout << node << " ";
    }

    return 0;
}