#include <fstream>
#include <vector>
#include <bitset>
using namespace std;

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

const int N=100001, M=500001;

int n, m;
vector<int> ad[N], sol;
vector<pair<int,int>> mu;
bitset<M> viz;

int main()
{
    fin>>n>>m;
    for(int i=0;i<m;++i)
    {
        int x, y;
        fin>>x>>y;
        ad[x].push_back(i);
        ad[y].push_back(i);
        mu.push_back(make_pair(x, y));
    }

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

    vector<int> st;
    st.push_back(1);
    while(!st.empty())
    {
        int nod=st.back();
        if(!ad[nod].empty())
        {
            int v=ad[nod].back();
            ad[nod].pop_back();
            if (!viz.test(v))
            {
                viz.set(v);
                st.push_back(mu[v].first^mu[v].second^nod);
            }
        }
        else
        {
            st.pop_back();
            sol.push_back(nod);
        }
    }
    for(int i=0;i<sol.size()-1;++i)
        fout<<sol[i]<<" ";
}