#include <iostream>

#include <fstream>

#include <vector>

#include <stack>



using namespace std;



ifstream fin("ciclueuler.in");

ofstream fout("ciclueuler.out");



const int NMAX = 1e5+5;

const int MMAX = 5e5+5;



int n,m;

bool v[MMAX];

vector <pair<int ,int> >a[NMAX];

stack <int> st;



int main()

{



    fin >> n >> m;

    for(int i=1;i<=m;i++)

    {

        int x,y;

        fin >> x >> y;

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

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

    }

    for(int i=1;i<=n;i++)

        if(a[i].size()%2)

        {

            fout << -1;

            return 0;

        }

    st.push(1);

    while(st.size())

    {

        int nod=st.top();

        while(a[nod].size() and v[a[nod].back().second])

            a[nod].pop_back();

        if(a[nod].empty())

        {

            fout << nod << " ";

            st.pop();

            continue;

        }

        st.push(a[nod].back().first);

        v[a[nod].back().second]=true;

        a[nod].pop_back();

    }

    return 0;

}