#include <bits/stdc++.h>

using namespace std;

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

int n, m;
vector <int> v[100005], ans;
vector < pair <int, int> > edge;
bool viz[100005];
int main()
{
    fin >> n >> m;
    for(int i = 0; i < m; i++)
    {
        int a, b;
        fin >> a >> b;
        v[a].push_back(i);
        v[b].push_back(i);
        edge.push_back(make_pair(a, b));

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

    stack <int> st;
    st.push(1);

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

        if(v[nod].size() == 0)
        {
            st.pop();
            ans.push_back(nod);
        }
        else
        {
            int nxt = v[nod].back();
            v[nod].pop_back();
            if(viz[nxt] == 0)
            {
                viz[nxt] = 1;
                st.push(edge[nxt].first^edge[nxt].second^nod);
            }


        }
    }
    for(int i = 0; i < ans.size()-1; i++)
        fout << ans[i] << " ";
    return 0;
}