#include <bits/stdc++.h>

using namespace std;

ifstream f("ciclueuler.in");
ofstream g("ciclueuler.out");

stack<int>s;

bitset<500005>viz;
int n, m, ind_perechi=1, a, b;
vector<int>graph[100005];
pair<int,int>perechi[500005];
vector<int>rez;

bool verificare()
{
    for (int i=1; i<=n; ++i)
    {
        if (graph[i].size()%2==1)
        {
            g << -1;
            return false;
        }
    }
    return true;
}

void euler(int ind)
{
    int sus, altnod;
    pair<int,int>muchie;
    s.push(ind);
    while(!s.empty())
    {
        sus=s.top();
        if (graph[sus].empty())
        {
            rez.push_back(sus);
            s.pop();
        }
        else
        {
            if (viz[graph[sus].back()]==1)
                graph[sus].pop_back();
            else
            {
                muchie=perechi[graph[sus].back()];
                if (muchie.first==sus)
                    altnod=muchie.second;
                else
                    altnod=muchie.first;
                s.push(altnod);
                viz[graph[sus].back()]=1;
                graph[sus].pop_back();
            }
        }
    }
}

int main()
{
    f >> n >> m;
    for (int i=1; i<=m; ++i)
    {
        f >> a >> b;
        perechi[ind_perechi]={a,b};
        graph[a].push_back(ind_perechi);
        graph[b].push_back(ind_perechi++);
    }
    if (verificare())
    {
        euler(1);
        rez.pop_back();
        for (auto &v:rez)
            g << v <<' ';
    }
    return 0;
}