#include <iostream>
#include<fstream>
#include<vector>
#include<queue>
#include<list>
#include<stack>
#define dim 100002
using namespace std;
ifstream f("ciclueuler.in");
ofstream g("ciclueuler.out");
list<int> nod[dim];
queue<int>q;
stack<int> st;
int v,vf,viz[dim],n,m;
void citire()
{
    f>>n>>m;
    for(int i=1;i<=m;i++)
    {
        int a,b;
        f>>a>>b;
        nod[a].push_back(b);
        nod[b].push_back(a);
    }
}
void bfs(int i)
{
    viz[i]=true;
    q.push(i);
    while(!q.empty())
    {
        int x=q.front();
        for(list<int>::iterator it=nod[x].begin();it!=nod[x].end();it++)
        {
            if(viz[*it]==0)
        {
            q.push(*it);
            viz[*it]=1;
        }

        }
        q.pop();
    }
}
int verificare()
{
    bfs(1);
    int   q=1;
    for(int i=1;i<=n;i++)
    {
        if(viz[i]==0 or nod[i].size()%2==1)
        {
            q=0;
            break;
        }
    }
    return q;
}
void sterge_pus()
{
    for(list <int>::iterator it=nod[vf].begin();it!=nod[vf].end();it++)
    if(*it==v)
    {
        nod[vf].erase(it);
        break;
    }
}
void ciclueuler()
{
    st.push(1);
    while(!st.empty())
    {
         v=st.top(); //extrag din stiva
        if(!nod[v].empty())
        {
             vf=nod[v].front();
            st.push(vf);
            nod[v].pop_front(); //sterg vf din lista lui v
            sterge_pus(); // sterg v din lista lui vf
           continue;
        }
        if(!st.empty()) g<<v<<" ";
        st.pop();
    }

}
int main()
{
    citire();
    int x;
   x=verificare();
   if(x==0) g<<"-1"<<"\n"; //neconex sau grad impar
   else
   {
       ciclueuler();
   }
    return 0;
}