#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;

}