#include <fstream>
#include <vector>
#include <iostream>
#include <queue>
#include <algorithm>
#include <stack>
using namespace std;
ifstream f("ciclueuler.in");
ofstream g("ciclueuler.out");
vector <int> G[100005];
int n,m;
vector <bool> marcat;
vector <int> grade;
void bfs(int nod)
{
    queue <int> q;
    q.push(nod);
    marcat[nod]=1;
    while(!q.empty())
    {
        int u = q.front();
        q.pop();

        for(auto x : G[u])
            if(!marcat[x])
                q.push(x),marcat[x]=1;
    }
}
bool conex()
{
    bfs(1);
    for(int i=2; i<=n; i++)
        if(!marcat[i])
            return 0;
    return 1;
}
bool is_euler()
{
    if(!conex())
        return 0;
    for(int i=1; i<=n; i++)
        if(grade[i]%2)
            return 0;
    return 1;
}
vector <int>rez;
stack <int> s;
void euler(int nod)
{
    while(!G[nod].empty())
    {
        int w = G[nod][0];
        s.push(nod);
        G[nod].erase(G[nod].begin());
        for(int i=0;i<G[w].size();i++)
            if(G[w][i]==nod)
              G[w].erase(G[w].begin()+i);
        nod = w;
    }

}
int main()
{
    int a,b;
    f>>n>>m;
    marcat.assign(n+1,false);
    grade.assign(n+1,0);
    for(int i=1; i<=m; i++)
    {
        f>>a>>b;
        G[a].push_back(b);
        G[b].push_back(a);
        grade[a]++;
        grade[b]++;
    }
    /*
    euler (nod v)
    cat timp (v are vecini)
       w = un vecin aleator al lui v
       sterge_muchie (v, w)
       euler (w)
    sfarsit cat timp
    adauga v la ciclu
    */
    if(is_euler())
    {
        int v=1;
        do
        {
            euler(v);
            v = s.top();
            s.pop();
            rez.push_back(v);
        }
        while( !s.empty() );

        for(int i=0; i<rez.size(); i++)
            g<<rez[i]<<" ";
    }
    else
    {
        g<<"-1";
    }
    g.close();
}