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

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


vector<int> G[100001];
vector<int> ans;


bool folosit[500001];
pair<int, int> muchie[500001];
int n, m;



void citire()
{
    fin >> n >> m;

    for (int i = 1; i <= n; ++i)
        G[i].reserve(20);

    for (int i = 0; i < m; i++)
    {
        int x, y;
        fin >> x >> y;
        G[x].push_back(i);
        G[y].push_back(i);

        muchie[i].first = x;
        muchie[i].second = y;
    }
}


void afisare()
{
    for (int i = 0; i < ans.size()-1; i++)
        fout << ans[i] << ' ';
}



void euler()
{
    vector<int> st;
    st.reserve(100001);
    st.push_back(1);

    while (!st.empty())
    {
        int node = st.back();
        if(!G[node].empty())
        {
            int e = G[node].back();
            G[node].pop_back();

            if (!folosit[e])
            {
                folosit[e] = true;
                int rez = muchie[e].first ^ muchie[e].second ^ node;
                st.push_back(rez);
            }
        }
        else
        {
            st.pop_back();
            ans.push_back(node);
        }
    }
}



int main()
{
    citire();

    ans.reserve(m+1);

    for (int i = 1; i <= n; i++)
        if (G[i].size() & 1)
        {
            fout << "-1\n";
            return 0;
        }

    euler();
    afisare();

    fin.close();
    fout.close();
}